tryed the NVagp module? it does support your motherboard.
To force the use of NVagp insert this line in the device section of XF86Config file:
Option "NvAgp" "1"
the default is "3" (uses AGPGART, if it fails uses NvAgp).
I warn you not to use the AGPGART module with the NvAgp.
best wishes (life isn't so much beautiful without AGP