SATA HD's may appear faster as they all have 8MB caches.
Most PATA HD's have only 2MB cache.
Premium PATA HD's came with 8MB cache.
If your system is pre-built, you most likely belong to the 2MB cache populous & you will notice a good increase in speed moving to SATA.
If however, you've been doing your own puchasing/building & have spent a little more for the premium drives, then you will notice no speed increase whatsoever.
Also keep in mind that SATA drives are a newer generation, and each successive generation of HD's is slightly faster than the previous, due to higher density of bits.
Be warned, you WILL need your SATA drivers on floppy disk when installing to a SATA (or raid for that matter) HD directly, otherwise windows XP will not know how to communicate with the SATA controller & hence will not detect the HD.
When you have made the disc, make sure you keep it safe. It's embarassing having to go to a friends place to get some drivers copied from a cd onto floppy so you can recover your system