Sorry for bringing back the dead, but I've been battling this with Terri's onboard video driver the past week as well. DP used to run perfectly a couple weeks ago and now it doesn't run at all. Tried old drivers, new drivers, still looking for the manufacture drivers(I don't know the manufacture so really I'm looking for the mobo box) but nothing seems to be working. The only thing I can think of would be that I installed DirectX 9.0c with another game recently, but I tried disabling Direct3D with dxdiag and that didn't improve things. If I uninstall the graphics drivers completely, it creates the 'You do not have an OpenGL card installed error...'. Within display properties it shows the S3 Driver specific tabs for the KM400/KN400 S3G Unichrome display adapter. The information tab shows the proper versions of all the drivers (Including OpenGL ICD) are installed and match up. The HKLM\SOFTWARE\Microsoft\WindowsNT\Opengldriver\ appears to be the correct vticd.dll driver.
I'll keep trying to see what I come up with though.