Hello and welcome to Bleepingcomputer.
The correct driver for Windows Vista 32 Bit is 260.99
Which is here.
The correct driver for Windows Vista 64 Bit is this one.
I see that your computer supports 64 Bit Technology, so that is why I supplied both versions.
As for what-ever other files you have on your computer, I suggest getting rid of those, make sure you un-install the original driver you have installed now, just so you know you have only the correct driver installed for this video card.
I would also suggest you take a look around your motherboard's BIOS setup utility for anything related to your graphics card's settings.
There may be settings here that are related to how the video card performs, without actually looking through your motherboard's owners manual, it would be difficult for me to make suggestions.
Also one last suggestion. I would take a look at the condition of the inside of your computer for dust issues.
Dust can cause over-heating issues and it is often over-looked as a possible culprit.
Please examine your cooling fans and heat sinks closely for embedded dust.
If you notice dust built up in the cooling fins of the heat sinks, you can purchase a can of compressed air, use the plastic straw and concentrate the blast of air into those heat sinks until all dust is removed.
See if this resolves the problem and post back the results.
Edited by MrBruce1959, 01 December 2010 - 12:57 PM.