Speaking of Media Player Classic, for the longest time (haha, I just realized I just repeated myself), I have also wanted to tell Windows Vista to disable the screensaver. It was annoying that whenever I was using Media Player Classic, it would start the screen saver after 30 minutes into the movie. I would then have to disable the screen saver temporarily and re-enable it afterwards. Similar with turning off the screen and sleep/hibernate options.
Anyway, while I was searching for something recently, I came up on Media Player Classic – Home Cinema. It appears to be a fork off the main Media Player Classic branch and one of the things it supports now is: Kick off Screen Saver from Power Options only while video is playing (Vista). So if you’re a fan of Media Center Player and dislike the fact your screen saver goes off when the video is playing, you should check out this Home Cinema version.