What version of Mesa are you using? Also, what process owns 0xcccc0000 -- I
assume X? The full dmesg would definitely be nice to have. What chipset do you
have (lspci -nn wouldn't hurt)? Does setting agpmode=4 or agpmode=0 help at
all?

Another idea -- add MESA_EXTENSION_OVERRIDE=-GL_ARB_framebuffer_object to your
system environment (make sure that the DM gets it).

FWIW, my personal experience with a NV34 (PCI-E) is that as soon as I open
chrome or firefox, it hangs hard; before then, no issues. And that's without
any sort of compositor/etc in the fray.