I am experiencing a problem very similar to:
I have two Dell 2001FP displays connected to a Dell GX270 Optiplex.
The video card is a dual headed GeForce FX 5200.
I'm running FreeBSD 5.2.1 with XFree86 version 4.3.
No errors are reported, however the display :0.0 never seems to sync properly.
(The :0.1 display works perfectly.)
The screen will blank every 30 seconds or so and running an app like glxgears
causes the problem to get much worse much faster.
I've tried the driver with and without the FreeBSD AGP module.
Can anyone comment on this problem?