I can't tell if the computer is picking up the USB at all during boot. Would the light turn on before the Windows boot screen if it were? If that's the case, it isn't, but otherwise I don't know how to tell. I'll try using a different USB stick and just installing Tiny XP, and see if I have any luck with that. Perhaps with a reformat, the problem will take care of itself. Perhaps not, though.
Thanks for the advice, I'll let you know when I know.