First off, use the newest version of UnleashX (0.36.0620A) Here's what you need to do:
1. Make a folder and name it InstallCD
2. Put the UnleashX (Newest version) default.xbe and config.xml in the folder "InstallCD"
3. Put your CDrive and EDrive folders in here
4. Edit the config.xml and find where it says <Menu> Just below this add this line
<Item Action="PrepareHD">Prepare New HDD</Item>
5. Use an ISO program for xbox to create a special ISO file. Don't use xISO. I recommend C-Xbox tools or Craxtion. Make sure you choose the UnstallCD folder to be the root of the CD so the ISO file has default.xbe in it's root.
6. Use your CD Burning program to burn your new ISO file.
Now your ready. Boot up the xbox with the stock drive in it. Then put in the CD. UnleashX should recognize it as an UnleashX cd. If you boot up your xbox with it in the drive, it should autolaunch the install cd.
7. Plug in your new HDD and start it up with your cd-rw. Choose prepare new hdd. Wait!
You should find out which bios you have for certain before you prepare your HDD because it will determine how your HDD is formatted. If you have the 4983.67 you will want to change to the 4983.06. The *.67 bios puts everything after 137gb onto the G drive, which on a 160gb drive would create a 23gb partition, which would be essentially useless. the *.06 bios puts everything on F. The only time you would need a *.67 bios is if your drive is more than 260gb, because shortly after this point it starts corrupting data. Also, many xbox apps either don't recognize the G drive, or else they don't handle it that well. For example, XBMC mounts my F drive instantaneously, but it takes longer to mount my G drive than it does to connect to a network share! If you want to know which bios you have, simply use the Bios Check app available in "the usual places."
Goodluck. If you need anymore help, press my buttons.