if you have/can get the eeprom you are in good shape to get this fixed up. you can either clone your existing hard drive with one of the clone utilities, or you can copy it all out via ftp. you will need a computer with a working IDE DVD drive(cd probably would work too) and your new hard drive. make a new copy of XBOXHDM with the EEPROM (in all caps IIRRC, either that or all lower case, one or the other, but it is case sensitive) in the eeprom folder. use XBOXHDM to format and setup the new hard drive (if you don't clone it) and then lock the hard drive via the eeprom. you should be able to swap the drive out no problem at that point.
( isee after a peroid you cant Edit still. )
xboxhdm did have a usb mode at a later point.. http://forums.xbox-s...22-usb-edition/