I actually recommend using VLC player due to it having most codecs and playing more files that WMP doesn't. Also, when installing codecs, becareful in not installing too many because eventually they will interfere with each other...I had that problem before...So far i have used VLC with no problem, running XP Media Center Edition and XP Pro.
Here is the download side, be sure to download the latest version.
VLC media player for Windows
If you need anymore technical questions, feel free to send me a message...I'm an IT Analyst, so I know a few tricks...THat goes for anyone that needs help too...