For linux there are 2 agp drivers one inside the nvidia kernel module (known as "nvagp") and another in the linux kernel (known as "agpgart". The drivers can use both those drivers but not at the same time ofcourse.
I wouldn't play that much with AGP on a MVP3 system (had one in the past). What I would do to get X running is the following if it really is an AGP problem. Add a line: Option "NvAGP" "0" to the device or screen section in your XF86Config-4 file. That will disable AGP.
AGP on these boards can be very instable.