[igalan]

When the computer shuts down, is there any event being recorded on the Windows XP event viewer?

And as bayoupimp says, the BIOS should fit in one floppy, the problem is when you try to store DOS to boot from it, and the utility to flash the BIOS. So modern motherboards can flash without booting the OS. Anyway if you see no way to do that, you can create a bootable CD-ROM or USB memory with as many files as you need.