Well, I hate to say it, but if you don't have a mobo BIOS update with mention of a fix for R9600 cards, you're probably SOL. Sorry.
I've had similar issues with my MSI KT4V-L mobo (KT400/8235) and FIC R9200 AGP 8x card. The KT400 was really the "KT333A", for the most part, re-named for marketing reasons. In fact, I've heard tell that Via later on sold KT400 chips as KT333As, they were a KT400 core, but AGP 8x was disabled in hardware. The fix for some people, has been to place a piece of transparent tape over a couple of pins to disable automatic AGP 3.0 (and thus AGP 8x) detection, causing the card to fall back to AGP 2.0 / 4x mode detection in the BIOS.
There was a BIOS update (1.9 or 1.A, I believe) for my mobo, with a specific mention of a fix for R9600 cards. I used to get "VPU recover" or "XP infinite loop in display driver" errors nearly weekly when using BIOS versions prior to that, but using that BIOS version or later seems to fix or work around whatever issue there is. Unfortunately, it also severely messes up my BIOS-accessable disk drives, so I can no longer access anything but the primary master HD on my Promise IDE controller in DOS mode. Which means no ability to use Ghost 2003 to backup my other HDs.
I tend to agree with a couple of the posts in that linked thread as to the cause.
A number of A7V333 and RADEON 9600XT users face these issues. Just visit the forums at viaarena. Nobody has a solution. This is a serious issue and needs to be fixed. ASUS, ATI and VIA, please solve this! A number of VIA chipsets screw things up when RADEON cards are used!
ugh. you may actually be in one of those sol areas with via and ati. i was in one of those with my 8500dv and a km400 motherboard.
my guess is that the hardware connecting the two devices just doesn't seem to get along. if i remember correctly older via chipsets did weird things with the agp driving strength and agp gart
I can only guess that the later BIOS versions for my board, did some tweaks to the memory-controller registers, or the AGP driving strength values, which are not normally user-accessable options in the BIOS for my board.