i had a similar problem, but i have to ask you something wich chipset is using your mobo.?? you said that is a VIA but it is a KT333 or KT400 ?? wich one?
i have a VIA KT400A and AGP 8x the only thig that i did in my XFree86Config-4 was add the line
Option "NvAGP" "3"
so when i boot my system try to use the AGPART and if that fails then uses the NVAGP.
now just work fine
My system is a MSI GeForce4 Mx 440 with AGP 8x VTD (MS - 8888)
MSI KT400A With AGP 8x
512 MB RAM
Athlon XP 2100+