PATA and ATA are the same, parallel ATA.
Older PCI/PCI-X G5s can't use the latest 10K 150GB Raptor on the native SATA ports, but no problem with your dual core G5s.
Seagate 7200.9 SATA drives had a feature implemented that prevented use on any G5 and some SATA controllers called "Spread Spectrum Clocking" or SSC for short.
Serial ATA or SATA or SATA-II is what you need.
FAQ Guide has a lot of information if you dig for it on RAID, SATA and where to find reviews, benchmarks and more.
You don't need to purchase anything extra unless your needs grow to more than two internal SATA drives.
One route would be to get that 10K Raptor which is the fastest boot drive or for building scratch RAIDs. Or affordable and larger and still good performance in 300 or 500GB drives. RAID is best done with two identical drives.