Gigabyte Pt880pro PCI-E related video problems

Hello, let me start by posting my computer's specs.

Gigabyte Pt880Pro-A7 Combo Motherboard
2.8Ghz Pentium D
2 Gig DDR (pc3200)
Ati HD4850 PCI-E
VIA 5.1 Audio
DVD-RW/CD combo drive
1TB Segate SATA
1000 watt PS

This is my "Build-up" computer. I just keep upgradeing components as I go.

Ok so on to my problem. While playing games, I get these graphical errors, as pictured below:



Is pretty much described as random textures popping up out of nowhere. And this happens in all of my games from Borderlands, to NFS:MW. This same issue happened with my previous HD4350 PCI-E card, but it did NOT happen when I had my X1550 PCI card.

Now, I notice that to temporarily fix this problem, I can switch resoultions back and forth and the textures dissapppear, but for a game such as NFS:MW, the maps are so big that this "fix" only works locally and other parts of the map are still plagued by these random textures.

I've also learned that my PCI-E slot is indeed only x4, not x16.

Now my question is, how can i permanently fix this issue without buying another mobo?