You mentioned the BIOS is from 1995, almost 11 years old, that would make
the board 11-12 years old. You also mentioned going from '98 to XP. If that
was the start of the problem, without installing the chipset drivers and
device drivers, that's probably the issue. I'm suprised that there are no
generic drivers on the XP CD that take care of your devices, although I
wouldn't expect to find every chipset driver, there are many generic drivers
in the CD to get you up and running.
To start with, the CD Rom that came with your motherboard. It should have
the drivers for the sound and video. If you can at least get up and running
with those, you'll be in better shape than now. A better fix would be to get
the latest drivers from the manufacturer's site.
As others have mentioned, it's most likely a driver, not a BIOS issue. If
you can get the system running without flashing the BIOS, it'd be better,
since a mistake could be costly. But an 11 year old BIOS...