(Wow, an Atlanta board! Yeah, finally!)
I second what lovinlovett has said. It also doesn't hurt to see what's playing at the Fox during your visit. Also check out the Aurora Theatre in Lawrenceville. The Aurora is one of the few, small professional theatres in GA, and I believe the only professional theatre in Gwinnett County.
To jazzy: I believe the last tryout production to come through Atlanta was SISTER ACT.
-- SDG