Windows Media Center Edition (MCE) is very similar to XP Pro. You shouldn't see much of a difference in performance. If you're not going to use the MCE part (recording TV) then it's kind of pointless to have it. From what I understand MCE is just XP Pro with a few minor features removed from Pro and the TV recording (etc) features added.
A 2Ghz proc with 1GB of ram should not run slowly at all, unless you're doing some serious video editting or other similar process. There may be something else wrong if that is the case. I run a 1.8 Ghz proc with 1GB of RAM and I'm using MCE. Runs like a champ (for windoze).
When you installed XP Pro did you do a FRESH install or install XP Pro OVER MCE? I would suggest the FRESH install (including formating the HD) if you didn't do that.
Also there is a particular order to install everything (the OS, Drivers, Programs etc). I don't recall exactly what order to do everything in detail. I'm pretty sure if you did a Google search on installing windows you could come up with something. I would also suggest checking out
MaximumPC.com and read some of their archives. I remember reading about the order you should install everything in one of their issues. Maybe they have the article on their site now.
Hopefully that helps a little bit. Maybe someone could chime in with some other suggestions.
MIKE B