Just spotted these 3 handy tips in this article from PCWorld

Handy Tips for Window Media Center and More - PC World

  1. 1. Stop Windows Media Center from Using Your Entire Hard Drive
    1. ‘Start Windows Media Center.
    2. Scroll down to Tasks, then over to Settings and click it (or press Enter).
    3. Choose Recorder, and then Recorder Storage. (Note that these options appear only if you have a TV tuner installed and configured.)
    4. Use the Minus arrow next to Maximum TV limit to decrease the storage (in 25GB increments) to the amount you want to allow WMC.
    5. Click Save to finish the operation.’
  2. 2. Make Documents and Media Open in the Proper Programs

“My preference is simply to right-click any file that's incorrectly associated (like, say, one of the aformentioned RTFs), mouse over Open With, and then click Choose Default Program”

3. Force Programs to Run Full-Screen

    1. ‘Right-click the program's shortcut, and then click Properties.
    2. This will open the Properties window with the Shortcut tab already selected. Click the pull-down menu next to Run and choose Maximized.
    3. Click OK .’

Rob