One of the nicest features of OS X is that you no longer need to purchase additional software to make all the type on your screen look nice and smooth. However, when people move from an older Mac system with a CRT and System 9, this smoothing can actually be a bit disconcerting until you get used to it.
Fortunately, there is a way to adjust this smoothing somewhat. Go into System Preferences and choose Appearance. Down at the bottom you’ll see “Font smoothing style:” with a pop-up window to the right. There are five options. Choose the one you like best. You can also turn off text smoothing for fonts below a certain size. By default this is 10 point, but you can try other sizes. Make sure you close all applications before you change anything. No changes will take effect until the next time you open an application. That includes the Finder, so you might just want to do a manual restart.