Your specs say 1066-MHz DDR3 DIMM non-ECC memory only. You may be stuck with that. Those proprietary dell systems are flaky about that sometimes.
that's what i'm worried about - dell proprietary. i was just wanting to know if anyone's attempted to do what i was going to do with 1333mhz chips. i've seen a thread where a certain dell system wouldn't boot any more due to the wrong ram chips, so i guess i'll go with 4x2gb 1066MHz chips from ramcity.