Can't install oldere OS.

My really really old Toshiba Libretto, for some reason it's got Windows XP running on it, and it's painfully slow, I tried installing Win2k, but I just can't get into the BIOS no matter how hard I try.

Anyway to get past this? Please note that I've already tried all available key combinations for the BIOS.

did you try
F1 or Del or F8 or F12. I thik those are only keys i've seen at start-up