Dan showed me this. In Windows XP, right click on the desktop and choose properties. Select Appearance, and then Effects. In the second drop-down box, change the font smoothing method from “Standard” to “ClearType.” Then click OK a couple times to dismiss the windows and apply the changes. It took me a while to notice the difference. Sure, it looks a little different, but is it better? After a day, I was convinced. For me, it substantially improves the readability of the text (content notwithstanding) and reduces eye strain. We’ve added it to the list of things to do to new computers before delivering them.

Cleartype is most noticable on LCD monitors. CRTs might show some improvement, but not as much. I guess it works with how LCD panels create each pixel with red, green, and blue transistors.
For the history buffs out there, this technique started with the Apple II in 1976:
http://www.cnn.com/TECH/computing/9812/08/cleartype.idg/