5100 Demension desktop? You may want to check out the asrock 4core dual sata II for $66.99 at newegg. It runs with ddr or 667ddr2 (pc5300). It will be a tight fit, and you will have to backup your files first and format the hardrive. Or you can bite the bullet and sell your old ram on craiglist and use ddr2 with a g31 motherboard, which are plentiful and cheap at newegg. Some are less then $50 shipped and come with a rebate. Foxconn boards are the most frequent brand used by dell.