I've transferred the BSP rendering code to use the new level loading code, so I can now display correctly-coloured Quake 2 levels. [smile] The Quake stuff is in its own assembly, and is shared by the WinForms resource browser project and the XNA renderer.
I'm also now applying lightmaps via multiplication rather than addition, so they look significantly better.
A shader solution would be optimal. I'm currently just drawing the geometry twice, the second time with some alpha blending enabled.