The fact that moving the mouse left that artifacting is a clear indication it's a digital issue.
Tantalums have two failure modes. Dead short or blown up. They don't gracefully drift out of spec and when they die they make it pretty obvious as you have discovered.
Keep all your VRAM pulled as you mentioned that it's happening with it removed. This narrows the fault down to bad onboard VRAM or a problem with the video chipset. If you can, find a copy of Snooper and run the VRAM test.