MCE *is* Windows XP Professional. The ONLY difference is that it's had the Media Center added to it, and it's had it's domain functionality crippled. Aside from that, it is the Professional build.
To further that point, you can buy MCE for 149, but pro costs 199. The reason MS crippled MCE is so that corps don't buy the MCE version for 50 less than the pro version.
So, to that end, if you have a network at home/work, wherever, and you want to participate in a domain (ie, turn your MCE into Pro with the MC added), you can perform the following hack to re-enable domain participation for MCE:http://www.extended64.com/blogs/rafa...icles/404.aspx
Voila. MCE is XP Pro with added Media Center functionality. Perfect.