derrmc has a point. Your current system supports ATA, so why not stick with an ATA drive? Now yer getting into boot issues, extra cards, and the possibility that if you got an OEM SATA drive, it most likely won't come with the cables you need to hook it up. (SATA drives use different stuff). Perhaps your SATA PCI card will have connectors with it. Yer still going to need to look at your power-supply, though. You'll be consuming a bit more power.
Just relax, though, and see what comes in the mail (or however it's getting to you). Like mentioned above, if you futz things up or run into problems, you can always swap in your old drive (or switch to another comp if you have one) and troubleshoot.
Oh, and as for your boot-order in your BIOS, that list just tells you where the system "looks" first for an OS or boot-up instructions. Floppy first, then CD-ROM, then hard-drives. Since you hardly use floppy anymore (under normal circumstances), I set my CD-ROM first, HDD second, and disabled the boot-checking for my floppy. (Some mobo's don't support deactivating a boot-check on a drive, though.)
