Windows Media Center is a program that provides a DVR like user interface to all of your videos, music, CDs, DVDs, photos, recorded TV, & FM Radio. It, itself, is a DVR, if you have a TV Tuner card in your computer. You can use it to schedule recordings for TV shows and movies. Any computer hosting Windows Media Center can stream content to other computers AND to Windows Media Center compatible hardware like XBox and XBox 360 (called Windows Media Extenders). In other words, you can stream content from your home PC to your big screen HDTV in the living room. This works quite well, but getting the connection configured can be frustrating, especially if your computer is on a different floor in the house than your XBox and TV. For streaming HD content, you’ll want a 100mb network connection or better.
Windows Media Center used to be an off-shoot version of Windows XP called Windows XP Media Center Edition. With Windows Vista, Windows Media Center came with Windows Vista Home Premium and Windows Vista Ultimate. With Windows 7, it comes with Windows 7 Home Premium and Windows 7 Ultimate.
Windows Media Center is great for archiving all of your home movies and using a Windows Media Center Extender (Like XBox 360) to stream your movies to your living room TV.