If you have an apple laptop with less than a gig of memory, or just a plain slow mac, you can still get a great recording with [b]Garageband[/b]!
The problem with slower computers (slow meaning low memory) is that in order to use wiretap or similar product, you have to be able to play all your voices at the same time, and this doesn't always work out if you have a lot going on in your score.
Perhaps you've tried exporting the MIDI to garageband and loaded up to VDL2 AU plugins only to discover that garageband takes up more memory than sibelius/finale and Kontakt Player combined, thus giving you a ";low memory"; error message.
[b]The answer?[/b] Use your notation program to get the dynamics and such to your specifications. Then export the MIDI to garageband. Load up the VDL2 instruments you want. Adjust pan if you wish. THEN instead of trying to play the song, goto File -> Export to itunes. It will mix down the song with all the correct sounds and toss it into itunes for your listening pleasure.
For more on VDL2 and Garageband, search the forum.