You’re not trying to shove that 3 GB/s through a PCI connection.Raptors are ATA150 which converts to 150mb/s and thats only a little bit faster than IDE.Still not a very effective upgrade though,i will agree on that.
Shocked that nobody suggested upgrading the processor.The Dimension 4500 supports northwood processors at 533fsb and the fastest one is 3.06ghz.2.8’s on ebay bring $50 = $75.