The gamesaves you add should be stock ones (never ran yet). That way when you install the new HDD it boots just like a brand new unmodded xbox. Then you mod it like you would normally (copy gamesaves from MC, load one of the softmod games and install). Including the gamesaves in the E:\UDATA will just cut out the step of copying them with a memory card/AR.
The only reason we say it's easier to build it as stock, there tends to be alot of problems usually getting it to load the hacked dash (usually loads the M$ dash), so by making it stock it makes less problems.
Steps I'd do:
1. Get a stock C and E folder (can be found in CASH, Slayers, AID)
2. Get your eeprom.bin
3. Put your C and E folders in the "linux" folder.
4. Put your eeprom.bin in the "eeprom" folder.
5. Run "make-iso-win.bat" to create the XISO you need. (use "make-iso-lin.sh" if your running Linux)
6. Hook up the HDD to your PM in your PC and put your XBOXHDM disc in as well as making sure your bios is set to boot a disc before anything else (some bios's will boot the disc without changing the boot order)
7. Run "xboxhd" and follow the easy onscreen commands.
8. Remember to lock the drive once your done. From the main menu you can use the option 3 or 4.
Only fresh on the brain since I did it last night for a friend