In the first instance I'm recording into Garage Band, but I have the opportunity for the track to be professionally produced. Obviously this would be done using ProTools. But rather than re-record each track for ProTools I'd like to be able to Export the entire song as a ProTools file.

any suggestions?

cheers,
Pootle

you need a program to transform mp3 into wavs?
you can import a wav file into pro tools...
I dont know for sure but you cant export a song or a track directly to pro tools...
But why dont you record in Pro tools?
I always record directly into protools before transporting it to an other program like cubase, wavelab etc..

Since GarageBand exports to iTunes, set iTunes to import as an AIFF file. Import each track or instrument seperately and then it can be ported to ProTools as audio tracks. Hope this helps