Is your hard drive still poking along at 1.5 Gbps? Samsung is now shipping one of the first SATA II hard drives with 3.0 Gbps throughput at about $93 for the 80GB HD080HJ, which is a nice, low price point for the consumer market.
https://gizmodo.com/maxtor-sata-maxline-iii-big-buffer-rush-16654
Seeing as how SATA I is still being adopted across the board, SATA II seems a little premature but if you simply must have your 1.5 Gbps, then be our guest.