If you've just bought a computer with Windows Vista installed and your fonts look awful, especially when browsing the web, it could be because the default settings enabled by the manufacturer have font smoothing disabled. Here's what the fonts look like without font smoothing:   And here's what they should look like with ClearType enabled:  

To make sure that ClearType is enabled, you'll need to open the classic Appearance Settings dialog. Right click on the desktop and choose Personalize. Then click on Window Color and Appearance:

If you have Aero enabled, you'll have to click on "Open classic appearance properties for more color options". Click on the "Effects..." button and make sure that your computer has the checkbox for font smoothing enabled.