Blackline Graphic Glitch on 7900GS?

Hello,
First time poster here. I have a IBUYPOWER PC with an 450 watt power supply, 2 gigs of Ram, AMD 4200 X2, with a Evga 7900GS 256 card. On older games like City of Heroes I have few problems but lately with higher end graphic games like LoTRs online and Everquest 2, I have been getting odd black line graphic glitches running thru the game. I've cleaned the fans, and removed the case from my desk to give it more ventilation and the lines have decreased but still occur enough to be annoying.
I'm assuming it's an overheating problem but wasn't sure if it could be something wrong with the card itself?
Not sure what my options are at this point and any advice would be welcome. I'm not much of a PC expert and I've never had any of my systems overheat in the past?
Do I buy a new card?
Can I add some type of cooling unit to the case?
Will a 7950GT or 8600GT run even hotter and cause more problems?
Do I need a new powersupply?
Thanks in advance.....

Yeah
I just downloaded the software to check temp. It's idling about 131 degrees Farenheit and going up about 20 degrees when playing EQ2. Is adding fans relatively simple for a PC novice or should I take it somewhere?

37$ is too much for a GPU cooling, try this link. It`s more quet than the zalman, or this link if you want to keep the price even lower. link this fan should do the job fine.