VIA Gart driver (4-in-1) causes boot error

I've been having a hard time with Windows 98SE lately... I've got an 8KTA3
mobo with Athlon 1000 and 256MB. I couldn't keep the Matrox G400 working
(rendering problems after a while in Mozilla and Acroread, to be specific),
so I threw in the towel and installed an nVidia GeForce2MX that had been
lying around. Well, Mozilla 1.4 still wasn't stable -- a resource leak
caused the system to run out of GDI resources after a while. Not sure of
what was actually causing the problem, I decided to update the VIA chipset
drivers, since I hadn't put in a new set since, oh, buying the board two
years ago. And I had done a reinstall (over the old) of Win98 last week,
to fix a different set of problems (InCD 4 not working; InCD 3 not
displaying test). So I downloaded the latest Hyperion 4-in-1 set and did
the install.

Well, now, when I boot, it stops and tells me that it's trying to load a
program that isn't there, that is requested by either the registry or
SYSTEM.INI: viagart.vxd. Fine, except that a shiny new copy of
viagart.vxd is right there in c:\windows\system where, I presume, it
belongs! There is no mention of it in SYSTEM.INI. The registry mentions
it once (searching using regedit), in a section that references a lot of
other vxd's. Happily, if I hit "enter", the system waits a few seconds and
then boots anyway.

So my questions come down to, a) Anybody know why this is happening, or
what to do about it, and b) What does the GART driver do anyway, and do I
need it? Thanks.