In lieu of further clarification I'm going to assume you are connecting your laptop to a television via the S-video output.
An S-video connection carries a video signal of 480 or 576 interlaced lines, depending on which country you live in. Viewing any modern desktop OS at 640x480 on say, a 30" screen is not gonna be pretty
Most video on the other hand, is either designed for standard definition (it was made to play on a TV), or in the case of HD video, is scaled down by the video player software.
Some things you can do to improve the quality of your PC desktop:
- Adjust the size of certain desktop elements such as icons, window borders & controls, etc.
- Use bigger screen fonts.
- Possibly even use a higher contrast color scheme, which might help on older TVs.
This is precisely why the interface in Windows Media Center and other such software is called a "30 foot interface."