I would think that you could simply save the iTunes library from the PC to either an external drive or burn them to a DVD as data (not as songs), then simply import them into the Mac iTunes. The Mac will import the PC formatted tunes and reformat them as necessary. Don't forget to open the Mac's iTune preferences to tell it in what file format you want it to import song files (MP3, AIFF, etc.).
I just purchased a new Macbook. My problem is that I have been using Windows (XP) all the time before and have 600 songs in iTunes. How do I convert these songs so that they can be used on a MAC?