This is a very common question people ask when they come across ClearType in Windows XP and Vista.
There are a lot of advantages when your shift over to ClearType on windows XP:
1> With ClearType the fonts on XP will have smooth edges, so if you want to change to smooth font edge in XP or as a matter of fact, even on Vista, then you should shift over to ClearType
2> The font display quality improves dramatically over the traditional fonts with Clear Font
3> Readability of the screen font improves in Windows XP and also in Vista
4> It enhances the appearance of the fonts on Windows XP and Vista.
Read how you can enable ClearType in Windows XP / Vista.