PC4200 RAM will run fine @ PC3200 speeds, you might still have a bad stick. Not sure what you can do in the BIOS, maybe someone with more dell BIOS experience can help, I;m pretty sure you won't be able to change any settings for your memory.
You can try running memtest:
You should be able to test 1 stick at a time. If bad, corsair probably will replace the stick or the complete set.