R3xx cards have had OSS 3D for years now (although it's only up to OpenGL 1.3 IIRC). The only question should be if Google Earth requires OpenGL 2.0+ or not.
I don't think it does... Also the card might be in a pretty good shape at that point. Namely VBO support might be getting in and DRI2 should definitely be in at that point. Hmm, I was under the impression r300 was at OpenGL 1.4 and nearing 1.5. The jump from 1.5 to 2.0 is *big* though. Probably won't happen before Gallium3D.