You can use dependency walker to see what api calls it's making.
If it's your graphics card that it's complaining about, then it's probably using IDirect3D9::GetAdapterIdentifier. Build yourself a fake d3d9 dll and override that function to return the details of an older card. You can download the source of one of these and strip out the oblivion specific stuff to save having to create a wrapper from scratch.
If it's your graphics card that it's complaining about, then it's probably using IDirect3D9::GetAdapterIdentifier. Build yourself a fake d3d9 dll and override that function to return the details of an older card. You can download the source of one of these and strip out the oblivion specific stuff to save having to create a wrapper from scratch.