Here is a compilation of info that I have learned in my 360 hard drive hacking time. Hope it is of some use to someone:
First off, the reason to do anything with your Hard Drive is not to copy games to your hard drive to be able to play them without a disc. This is not possible yet, so stop asking. I am sure most people here are sick of hearing about people asking about that even though it is posted in several stickies!
The reason to do this is to backup your save games and/or to put a non Microsoft hard drive in your 360 without paying the huge price MS is charging for it.
Most items you download from xbox live are console or profile locked, so dont think you will be able to copy all those live arcade games you bought to your friends 360. You could do that, but they would just show up as a demo game unless the profile who bought the game is signed into live on that 360.
You will also not be able to edit any files to give yourself gobs and gobs of money or such things. Almost all the 360 files are signed and cannot be edited without destroying the checksum and it will just show up as corrupt.
As far as I know, you cannot copy a save game from one profile to another, or from your friends 360 to yours. This used to be possible but M$ put an end to this with a dashboard patch. It might still be possible on some games, but for the most part, it will not work.
You will be able to backup your saves so if your hard drive dies, you should be able to get them back. You will also be able to copy some xbox1 game saves over to your 360 but that is beyond the scope of this post.
You will be able to look at the 360 files and extract info out of it to examine, like wmv files. A program called x360 tool located on this site will let you do this. You will them be able to play them on your PC. Although either my 2.4G computer is getting too slow or it uses some strange codec, the video files stutter a bit. Not too bad though.
I have also had success copying my CD music that I ripped on the 360 so you will also not have to do that again if you have a hard drive failure.
If you plan on trying to pit a 120 Gig hard drive on your 360, then get Xplorer xtreme 2(google it). Thanks TheSpecialist for this mod, and Roofus and AngerWound for the original Xplorer360. Great Job!
Get the Via VT6421 PCI SATA card for best success flashing a DVD drive and reading and creating a working 360 hard drive from a Western Digital BEVS drive. You might have success with other cards, or built in SATA chipsets on your motherboard, but this is the one we know works. I even had problems with the VT6421. I had to go through 3 computers before I found one that HDDHackr and Xtreme360 would work with. So if you only see partition 0, try another computer. So save yourself a lot of problems and just buy that one.
I also have a cheap USB to SATA adapter that I am now using with Xtreme360 and it works great. But once again, it only works on 2 of my 4 computers. You cannot use this with HDDHackr as that runs from DOS. But if you are just looking for something to read and write to your original hard drive, this might work for you.
I could not get Xtreme360 to do a total backup and it appears it is because it has a problem with st.db file that is in the partition 3\Compatibility\Xbox1\TDATA\FFFE0000\MUSIC folder. You also cannot copy just this file as you get an error with Extreme360. You could delete this file and it will probably work. I did that one time. Xtreme360 complained about deleting it but did it, and then a full backup should work. I have not tried it since then. I just manually copy individual folders and files and dont worry about the whole backup option.
Be careful if you try to copy a big folder like partition 3 all at once. It appears that Extreme360 extracts everything to a temp folder first and then copies it to where you want it, so you need twice as much space available on your PC then what you are trying to copy. In partition 3\content\0000000000000000 is where all your downloaded content it placed. It is pretty cryptic, but I would suggest you delete all the demos and movies/trailers that you dont need before you make your first main backup as this will save you space and time.
If you try to convert a Western Digital BEVS 120 Gig drive to a 360 compatible drive, do not use the hddss.bin from your 20 gig drive or it will only be seen as a 20 gig drive after you are done. Also on that note, do not do a restore of a full backup of your 20 gig to your 120 gig or the same thing will happen.
HDDHackr will only work with Western Digital BEVS drives. Read the readme with it and it will tell you that. HDDHackr is flashing the firmware on the WD with a copy of your hddss.bin to fool the 360 into thinking it is the official drive and HDDHackr does not work with any other drives. If for some reason it was able to enable flashing on another brand of drive, it most likely screw it up so bad that it might not be able to even be used as a PC drive again so be careful.
Along the same path, make sure to save the first undo file that HDDHackr makes, as this is what will be needed to restore your drive back to a normal PC usable drive if you want to. After running HDDHackr the first time, I would copy that file off of your DOS boot disc or USB drive or whatever you ran HDDHackr from to somewhere safe. Email it to yourself or whatever, just dont loose it!
I am using one of the cheapest options of hooking the 360 hard drive to my PC with the Team Xecuter HD Adaptor. No frills but it works fine. This adaptor has a usb jack on it also. Dont be mislead about this jack. It is not to read from the drive, you still have to have a SATA cable on it. Its use is to power the hard drive instead of using the standard 4 pin power connector that can be plugged onto it. There is a warning that it is to be used only to read from your hard drive as there is not enough power to write to your hard drive using that. I have never used it so do so at your own risk. My USB to SATA adaptor came with its own power supply so I use that and risk any problems. Remember, a USB port is only rated at 500 ma and is not designed to supply a lot of power. That is why some external hard drives come with two USB cords, so you get twice as much power, in theory. I would not plug this into a USB hub unless it is a powered hub. You could use the one you got with your Rock Band game. You do have Rock Band dont you???
Be careful with your SATA cables. I read somewhere they are only designed to be inserted and removed 50 times so be tender with them and you should be fine.
And last but not least, Xport is another program designed to read your 360 hard drive but it is made to work with Datels XSATA and X-Port adaptors. I have not been able to get it to work with my cheap USB to SATA adaptor. I tried adding the USB VEN and DEF settings into its driver ini but with no success. If anyone has gotten this work, please tell me how. Both of these devices are supposed to make backing up info much easier as the Xport program lists games by their name instead of a cryptic 8 digit hexadecimal number like you will see with Xplorer360. Both of these are more expensive then the way I went but still a great value considering all the hours of gameplay you have spent getting as far as you have on your 360 games that you can loose if you dont have a backup. Your call.
Anyway, I hope this info has been helpful and if anything is incorrect, let me know and I will change it. I hope all the info I have compiled helps some others out in their 360 hacking.
Thanks to xbox-scene for a place to post this and to everyone else who has posted or wrote an app to help out us non-programming types out there.
Good Luck and may the Ring of Death never show its ugly face on your 360!!!