NVidia's tool is a vertiable pain in the ass. Get and use xNormal instead, it can also bake various things (like Ambient Occlusion and the textures of the highpoly version) to the lowpoly texture so you can get some effect even before Spring supports normalmaps. The first two models here have normalmaps made with xNormal.

Spring uses fragment (pixel) shaders already (unless you run in lowest settings).

It's just that we haven't added bumpmapping to them

Exactly

I don't think it'll take forever for you guys to do that...

Yes but currently there's no way to feed anything like a proper dot3 bumpmap into the system, not even a flexible material definition that could just get another tag. Save it for the next model format.