Let's see if we have any other configuration details in common:
Dual 1 GHz P3
Intel 840 Chipset
eVGA Geforce FX 5200 Ultra
Dell 1701FP connected via DVI
/proc/driver/nvidia/agp/status reports AGPGART 4x Fastwrites and SBA disabled
The FX 5200 definitely seems to be common among all the threads I've found about this issue.