See Selection Info in ITunes 9
Here's a quick iTunes 9 tip that may make your life easier if you burn a lot of CDs, or otherwise need to know the size of a selection in iTunes. In older versions of iTunes, if you wanted to know the play time for a group of songs, you had to drag those songs into a new playlist.
In iTunes 9, that step is no longer necessary. Simply select your songs (using any combination of click, Shift-click, and Command-click), and as your selection grows, the status display at the bottom of the iTunes window will update in real time, showing the item count, total play time, and total size of your current selection.
If you're trying to fill a CD, either based on data size or minutes of play time, this new "live" status display makes it a much simpler process.