I have four Dell Dimenson 3000 desktops with only 256mb RAM. I want to increase RAM with at least 1GB RAM each. I purchased four-1GB sticks of "CORSAIR XMS 2GB (2 x 1GB) 184-Pin DDR SDRAM DDR 400 (PC 3200) Dual Channel Kit Desktop Memory Model TWINX2048-3200C2PT" and now I understand that this stick is NON-COMPATIBLE with my computer. I performed a 'memory search' on Cosair's website and it only came up with one 1GB stick that IS compatible: VS1GB333, DDR-333 (PC-2700). BUT, an examination of the RAM in the computer already reveals it is a 256MB of DDR-400, PC-3200U. Question: Why does a stick of DDR-400, PC3200C2PT NOT work and why does Cosair's site suggesting a stick of DDR-333, PC2700?? Question: What RAM SHOULD I get to upgrade my four desktops from thier existing measly 256MB RAM existences??