I have an older dell xps gen 3 computer. I would like to upgrade it from two to four gigs. The manual spec. are as follows: Type: 400- and 533-MHz DDR2 unbuffered SDRAM Uh... whats that mean? Would either of the models below work? G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail Kingston 2GB 240-Pin DDR2 FB-DIMM ECC Fully Buffered DDR2 533 (PC2 4200) Server Memory - Retail Thanks for any help you can give!