Avoid Vista, unless it has something that XP does (which... Vista doesn't have...).
SATA is much faster than your old IDE drive. The interface itself is way faster. I used to have an IDE drive and when I went to SATA everything was leaps and bounds faster. I don't even have a high-performance HD system. Those 10,000RPM drives sure to look nice, but cost too much!
Anyways, if/when you can, get your primary drive up to a SATA drive. That would mean installing windows again, and you'd have to authorize again anyways (fresh install). If you have an internet connection you can just do it electronically, which is much faster than doing it on the phone.