soundfonts won't play

I'm trying to use sf2 files in GarageBand, and discovered that they can only be used while the track is playing. If you stop the track and restart, or return to the beginning of the song, nothing plays. You can't export the song using them, either.

Is there any way to convert sf2 files to some type of file that can be used in GarageBand?

Can exs24 files be used directly in GarageBand? If so, how? If not, what good are they?

Thanks to all for your help.

Mac OSX 10.6.8, GarageBand 09 (but the same problem on my wife's GarageBand 11).