SCSI will get you the fastest access times on the market and the only thing you'd need is an add-on card, preferably with an onboard BIOS. Ideally, you should have an SCSI HDD for your OS, apps and page file, and a SATA\PATA drive for the rest of your stuff.
However, let me remind you that if you have no experience with SCSI drives I suggest you do some homework. Read about SCSI Host Adapters, SCSI types 1,2, and 3, Single Ended, Low Voltage Differential, High Voltage Differential, setting SCSI IDs, and SCSI Termination. Mixing SCSI with IDE is another challenge. By default the IDE drives are assigned letters first. If your BIOS allows it, you can choose to boot SCSI first, making it the boot drive. You must read the host adapter's requirement for SCSI ID to make it the boot drive. It's usually 0 or 6. Read and learn. Unlike IDE, if a SCSI device is cabled incorrectly you will damage it. Also, you need to manually install SCSI drivers during Windows XP Setup so it detects your drive.
The above, although complicated, will get you super-fast performance. If you feel you're not upto the task, then go for the Velociraptor instead. Forget the SSD, it's a waste of money.