I check the recording of heat, and the temperature stays at a constant
52 degrees celsius. I have approximately 14 fans in my case, and with
the side cover off it stays at the same temperature as when it is on.
As far as power supply goes, I have an Antec 550watt Silent PSU. I
don't have issues in any other type of application (Game, rendering,
prime factoring), only in 3dmark03.

14 Fans!?!?! Cripes... maybe the card is getting blown out of the AGP slot!

Try gettting rid of some of the fans!