NMI: Parity Check / Memory Parity Error every 7-30 days

Hello,

We have a small office desktop that is blue screening, Hardware Malfunction NMI: Parity Check / Memory Parity Error.

This happens once every 7-30 days.  We are at the point were its not worth the trouble and are looking to purchase a new pc.

Configuration:

DELL Optiplex 360
2gb
core 2 duo
Latest Bios rev.
Windows xp Pro SP3
Onboard video
Geforce FX 5200 256 PCI w 2 VGA out (installed this card after market - latest drivers)
Three monitors in use
255W power supply!?!

When the system crashes, the onboard video monitor locks up, and the two geforce 5200 screens display the BS error.

Tested RAM multiple times with different programs.  OK
Replaced with new Geforce fx 5200 into a different pci slot
have not messed with BIOS

I want to take that geforce out and restore the computer to original specs.  The problem is, it can go a month without any issues!  We have the fx 5200 in 14 other systems with no issues.

It is stilled warranted by Dell.  Should I put up a fuss and get them to send me a replacement?

THANKS!

Matt