Looks like you have a bad stick of RAM.
Although the corruption could also be from the Graphics Card's memory or the CPU.
If I were testing I would try a new stick of RAM. If the problems persist I would try a new Graphics Card. If the problem persists I would try a new processor.
If I read your specs correctly you have one stick of 512 RAM.
Your board:
http://www.asrock.com/product/product_p4vt8%2B.htm
Can handle:
Memory Max. 3GB
3 x DDR DIMM slots,
DDR 400/333/266
This scan will fill you in on more details:
http://www.crucial.com/systemscanner/index.asp
Considering the warranty I would take it back unless you have an interest in learning
do it yourself computer building.
Either way I believe you have some hardware that needs replacing.