Dang dude!
1. Do you have the correct cable (80 wire) on it?
2. Is it modded or rounded?
3. Is the hardrive alone on the cable? (no cd, dvd etc..)
4. Is the blue end plugged into the mobo, and the black end on the drive?
5. Check device manager, XP likes to change the DMA settings for you...(It's not a bug, it's a "feature"...yeah right, Billy.)
6. Have you tried another brand of benchmark? Sandra's not exactly a lady on some systems.
Try these, and I hope they help!