I had the same problem with an older computer of mine - if the keyboard works (not if it's recognized, if it works
anyway) then just complete the install with the keyboard
It's not wonderful, but it can be done. That's what I ended up doing, and when I rebooted after the installation everything worked fine and I concluded that the install disk was just screwed up like that.
If the USB keyboard doesn't work at all, borrow a PS/2 one and see if that works...if nothing seems to, then yikes and I wish I could help you, but I have no idea :-/