There are a lot of users with this problem.
I'm not realy a linux user but you might try the folloing in the device section.
Driver "vesa"
VendorName "ATI Technologies Inc"
BoardName "Chipset ATI Radeon 9600 AS (AGP)"
BusID "PCI:1:0:0"
Option "TVOut" "1"
Option "TVStandard" "PAL"
Option "TVOutFormat" "COMPOSIT"
It works with ati 9600 agp card. if you look in the xorg log the card is detected as ATI but then again all current supported variants of ATI are detected on startup.
The proof of this is that i'm sitting in front of the tv sending you this.
Just make sure you have the right standard. This worked without setting any hsync or vsync and has full colour depth (24). This may only apply to uk users and or FreeBSD. The best advice is to suck it and see.
Yes I'm a freebsd user and no i'm not tying to convert anybody and I chose it because it runs on any old crap (Xbox) even the card board box it came in...
Good luck