XP pro has a few more options mainly to do with networking over XP Home.
I dont think that you would really benefit from anything that it offers over Home.
Media Centre lies somewhere inbetween Home and Pro, although some say it is XP pro, with the addition of an extra program that you can run once you are in windows called Media Centre.
I dont know why MS dont offer Media Centre as a seperate program that you could install to XP Home or XP Pro.
The Media Centre part allows you to organise all your Audio, Video and Photo files in its own library and has a nice, modern looking interface.
If you have a TV card in your pc then you can watch TV and use it as a PVR.
It is a nice addition to windows, although I dont use the library part as I have never got around to setting that part up.
If you do set it up then it searches all your drives and locates any media files and makes them readily accessible through various search terms such as name, genre, artists name, alphabetical and possibly some others as well.
Your PC should run Vista ok, I have forgotten how much ram you have so you may need to increase that as it runs ok on 1 gig but people say its a lot better on 2 gig.
Vista Premium and Ultimate both have Media Centre included, I am not sure which of the others have it, the business version doesnt have it.