Video card is artifacting. Happens. If its a Radeon you should use the drivers that came with your cd. Ive heard ATI has had minor artifacting issues with the drivers. Also, it could be your graphics card overheating. If you have OC'd the video card maybe you should return it to normal settings. Hope that helps.
Aspire X-Navigator Series
Intel 3.66 Ghz Dual Core
2x 1GB Kingston 4-4-4-12 Ram
ECS P4M890T-M2 LGA 775 M/B
Nvidia Geforce 7900GTO 512 MB PCI x16
Rosewill 700W PSU
Seagate Barracuda 250GB 16MB 3.0gb/s