Wing Commander Fowler,
Think of a hard drive as a water pump. Most hard drives pump water at 36 gallons an hour.
If you have an ATA-33 hose, so the pump can only pump 33 gallons an hour.
Then you put in an ATA-66 hose, the pump now can only pump 36 gallons an hour.
Then you put in an ATA-100 hose, the pump still can only pump 36 gallons an hour.
Then you put in an ATA-133 hose, the pump still can only pump 36 gallons an hour.
Then you put in an SATA-150 hose, the pump still can only pump 36 gallons an hour. (The PCI Bus can only run at a max theoretical limit of 133, so you will not get SATA-150 out of a PCI Card SATA Contoller.)
If were to buy the Western Digital Raptor 10,000rpm SATA Hard Drive, then it is worth going SATA. It is much faster than any 7200rpm drive.
If you currently have a 5400rpm drive in your computer, then getting Western Digital ATA-100 7200rpm drive with an 8Mb Cache, is also a good upgrade and cheaper than a Raptor Drive.
Take Care,
Richard