I'm a newbie who is in final mixdown mode of his 1st demo. I've used Mac's GarageBand app for all of the recording. Also, I've just installed Logic Express 7.2 but have yet to use it. My questions are these: How do I get a GarageBand file to a Redbook audio file? Will transfering the GB file to LE 7.2 first make it any easier?
Any other related info/advice would be helpful as well! Thanks!

Go to Share --> Send Song to iTunes

This send a 16bit 44.1 file to iTunes, aiff format. I'm pretty sure this is what you want.

I'm just making the transition to LE 7.2 as well, but I'm coming from DP 4.6 and I've played around in Garageband 3 for a couple months. I like the simplicity for home recording, but I cannot live with some of the GB limitations.