The problem is NOT the drivers in combination with an Athlon XP1800+ CPU. I have that exact setup, and I have no problems with framerates in glxgears whatsoever.
It might very well be the GF2 MX card -- those are fairly slow. I don't think they're quite that slow, but they are old.
I have 256MB RAM (PC2700), and I am using the 2.4.20 kernel, which disables the Athlon's speculative caching (which was the cause of the AGP bug that you were referring to, Wolfman -- the CPU will take control of AGP memory with regard to the cache, when the instruction stream only reads it, instead of writing, and if the video card later updates the same cache line, problems arise). 2.4.19 was actually the first kernel.org kernel that fixed that problem, though I believe it was included in RH's patches.