You can find a similar softsynth. I have not used garage band, but I do know when I installed logic it installed a bunch of garage band instruments and loops. They should be viewable from the file viewer on the right-hand side of logic.
Thanks, I don't see a way to use the instruments in logic. When I open the garage band song in logic it plays as it would in garage band, I just can't figure out how to import the one file.