I appreciate your input horus. I know OP corrected you on a few things, but I'll answer one or two of your points. I am certain the drive is an IDE drive. I used to pick up hard drives when they would have a good sale at my favorite electronics store (Fry's Electronics for those on the US west coast). I had one last one laying around and didn't want to waste it even though it's IDE. I'm also certain my motherboard supports both IDE and SATA. I could just re-install everything onto the new drive when I get it, but I really don't want to go through that (plus the IDE drive is working just fine). I probably won't get the 3TB, but the 2TB is plenty big as you say. I suppose I should break it up into multiple partitions as you suggest, but the only stuff I plan to put on it is music and maybe video. The existing 500GB drive is plenty enough to hold my personal documents. My home partition on it is 420GB and I still have 90% of that free.
Yup, it sounds like you know your system pretty well. There won't be a problem with running both types that I know of, but you may notice a difference in performance from one drive to the other... these can generally be accounted for by differences in data transfer rate, access time, and platter speed (but you probably know all that).
You might locate a smaller SATA drive and test your system with it before taking the plunge, though. (Maybe borrow one from a friend for a little while?) Or are you already using the SATA controller for optical drives?
Definitely give some thought to your partitioning scheme, if only to make it easier to plan your backup strategy down the road.
If the difference in price between them is favorable, the 3TB might be a better way to go, but I've not had the pleasure of playing with something that size myself, so I don't really know (my biggest drive is presently a 750GB USB).
Stay frosty, y'all. I gotta go bunky now. Talk at ya tomorrow, or...