I've said this like 9 times already, yet noone seems to listen to me even while I have an Action Replay and I need to do this. The problem is the FATX filesystem would get corrupted, so the Action Replay system does a few simple checks, however when you think, they don't do much.
If you get an "Invalid save error" what you need to do is unzip the file to a temporary folder. Then, make sure all thats in there is a UDATA folder (No readme's etc.). Inside the UDATA folder make sure there's only a folder with numbers (This is the game's personal savespace). In that folder, there should be only one folder with a few numbers, and possibly SaveMeta, SaveImage, TitleMeta, or TitleImage XBX. After that, the folder with numbers can usually contain anything.
Those XBX files are so the Xbox saves manager can display the little images and names of the saves. Note: Somehow you can edit these image files. I got a save off the net once and instead of the Halo logo it was a naked chick

.
Other than that, thats it! Zip the UDATA folder and drag and drop into the middle window of the Action Replay software. It should detect it and accept it as a save, ready for transfers.
Examples Of Bad FoldersBad Files In Base Of Zip.
Bad Files In UDATA.
Bad Files In First Number Folder (SaveSpace).
Examples Of Good FoldersClean Base Of Zip.
Clean UDATA.
Clean First Number Folder (SaveSpace).
Example Of The End GameSave Folder:In this folder 'anything goes' as it isn't checked. Make sure it contains a SaveMeta.xbx or it might cause problems though.
Shmoke and a pancake? Bong and a blints?RiceCake's first how-to thingy...Update: 12/29/03: Modified to use XBox-Scene's main server which contains better images.