Well, I know of a way, but it's nuts. My dad devised this idea.
It's been four years, so I'll do the best I can to remember.
He set BIOS to boot off floppy as first device. Then, using a working computer with XP and 2000, he created a bootdisk with ntldr, boot.ini, etc. So, if this floppy was in the drive, you would get a boot menu with 2000 and XP. If not, 98 came up as normal.
I don't recommend this idea (esp. since I can't quite remember how he did it), because of its inconvenience to you. But, it is an option.