Although you can finally play video files based on codecs like DivX in Windows 7's Media Center, without using alternative plug-ins* and possibly introducing codec hell with extra codec packs, you can't fast forward these videos in Windows Media Center. This is a stupid oversight but it is typical of Microsoft -- half-implement a feature and call it a day, thinking that people will be happy to have something rather than nothing. This kind of thing works for Apple because they update frequently, but when you take 3 years to deliver an operating system update and don't implement new features in between, the initial excitement over the feature is replaced with a feeling of tedium after a few months.
If my $50 DVD player can play and fast forward DivX files, why can't my much more expensive Media Center with its much more flexible software and much more powerful hardware? This value equation has repeatedly been ignored by Microsoft with Media Center.
Anyway, I recently learned about a way of jumping around within these non-Microsoft video files in Windows 7 Media Center without installing anything extra.
While playing a video, you can enter a time in minutes using the remote control and press the Play button to jump to that point in the video. Typing 10 and then Play will jump to the 10 minute mark in the file, for example. Also, it looks like you can multiply existing functions. So, if you type 10 and then push the skip button (which skips forward 30 seconds in the file and does work with these video files in Media Center), it will have the effect of skipping forward 30 seconds, 10 times -- 300 seconds, or 5 minutes.
So, it's not ideal, but it's better than nothing. Or, rather, it's better than trying to go back to that point 1 hour into your video by pressing the skip button 120 times.
* the alternative plug-in is Media Control, used in conjunction with the FFDShow codec pack.