If its a Hitachi, it has to be put into Mode B before flashing. Try reading some tuts on them. You have a variety of options for Mode B, Slax, Two-Wire Trick(a little dangerous, gotta be careful), JungleFlasher can put them in Mode B too.
If its been flashed before you can open the drive, unplug the xbox, plug it back in, turn it on, and hit eject. If it takes two presses to open, its in Mode B and can be seen in Windows.
Hope this helps, and remember, once you dump your key, save it in as many places as possible. Burn it to a cd, put it on a flash drive, on multiple computers, whatever it takes, just make sure you save it.
And download iExtreme 1.51 with the FW that corresponds to your Rom version. Easiest thing to do is look for a download that has all the iExtreme FW's. That way you know you have the one you want.
