Athlon XP 3000+ & ATI 9800 Pro AIW VGA problems

[mhon72]

Hi there,
I'd like to pick the collective brains of the forum.
My system includes:

Athlon XP 3000+ 400Mhz FSB
ASUS A7N8X Deluxe MOBO + Zalman CNPS7000B Al/Cu CPU cooler
2 x 512MB Samsung PC3200 DDR RAM (400Mhz)
ATI 9800 Pro All-in-Wonder 128MB 8xAGP VGA + Arctic Cooling VGA Silencer cooler + BGA Ramsinks
2 x 200GB Maxtor (7200RPM) Hard Drives
17" NEC 1760NX LCD via. DVI
Windows XP Pro

I've been running this system for a number of years now with few if any problems.
However, lately it has been playing up. The display on the monitor fails, all I get are garbled fragments on the screen. The system is still functioning but the monitor is obviously getting a duff video feed. I'm driving blind when this happens.
When I reboot the screen becomes fragmented at the Windows XP boot screen.
Having upgraded the video drivers to the latest ATI Catalyst 6.9 version I have noticed the memory chips on the VGA card getting quite hot. I subsequently reinstalled an older driver from a year ago but it appears to have done little to cool the chips.
My only solution to get the system running was to underclock the CPU. I was originally running at 200Mhz with a 10.5x multiplier, I can now only run as far as a 7.5x multiplier at 200Mhz. Any higher and the display becomes all jumbled.
Checking the BIOS and using the ASUS MOBO utility my CPU is running at a comfortable temperature in the low forties and the MOBO sensor is in the mid-twenties.

My question is whether it is my VGA which is causing the problems or the CPU?
Forgive my ignorance but does underclocking the CPU reduce the demands on the VGA card as well?
Any easy (read: cheap) fixes?
So if is it a new VGA card then any recommendations? The ATI X800 XT AIW has similar features to my 9800 Pro AIW which I'd like to keep. Anyone had experience of these?

Thanks for your time. Look forward to your comments.
Regards,
Mike