I have a problem with font antialiasing on a Windows XP PC. Example image (top half bad vs bottom half good taken on another XP box):
I'm using normal antialiasing (I don't like ClearType).
What could be causing this?
If this only happens in IE and not your desktop, IE may still be using ClearType. There is a setting under Internet Options | Advanced tab | Multimedia | "Always use ClearType for HTML*".
This setting also affects HTML emails in Outlook.
I'm one of the lucky people that can't stand the ClearType and strive to turn it off. However, you can also tweak how ClearType works using this site and ClearType Tuner PowerToy. (After tweaking I can make it acceptable for my eyes, but I hate doing that for every system I touch.)
I hope these tweaks help.
If this is happening everywhere, not just web browsers, you probably have ClearType enabled for all font rendering. To disable in in XP (where '>' means to click the menu item, tab, or button):
Start > Control Panels > Display > Appearance > Effects > uncheck "Smooth edges of screen fonts"