I had the same problem.
I posted this message on www.k7m.com and it helped alot of ASUS K7M owners (including me)
If you got a ASUS K7M MB with an Athlon processor and any kind of Nvidia graphicboard, do like this.
Install the Nvidia Reference 3.78 drivers then reboot into safe mode and copy nv4_mini.sys from the Nvidia 3.66 reference driver set to their %system_root%\system32\drivers.
So you need these files:
NV4_mini.sys ver 3.66
NV4_Disp.Dll ver 3.78
NVoglnt.Dll ver 3.78
NYInstNT.dll ver 3.78
Anyhow. You can find the drivers at http://www.reactorcritical.com/
/DjStef