"Is there any form of compression that works correctly and produces good image quality on the nvidia geforce chips?"
Yes, DXT3 DXT4 and DXT5 all look very good, DXT2 looks quite a bit better then DXT1 also.
"If id didn't compress lightmap textures or whatever they weren't supposed to compress, would the quality of tc be equal on all cards?"
id fixed that with the latest patch. The whining that you hear from most non nV owning gamers is the sky in Quake3, and that is it. Out of every game out there, and even in Quake3 itself, the only thing I have seen complaints on are the sky in Quake3(at least, running the latest patch). Switching over to using any of the other DXTC formats aids quite a bit(2 less so then 3, 4, or 5). Pretty major stuff