Use the open source radeon drivers and specify the
Option "AGPMode" "4"
in your xorg.conf.
(Consult xorg.conf and radeon man pages as necessary)
Yes, ATI/fglrx do suck; radeon driver is a bit better. the open source drivers don't have hardware rendering, but hey, neither does vesa. DRI with glxgears ~2500 should be attainable fairly easily depending on how the 1800+ handles it.