Tony, a ready to use arranger feature...thats one thing they left out of Garage Band. But its possible to create multitrack arrangements much faster than say a sequencing software etc. can. Ofcourse, it has its limitations but its possible to simulate the arranger`s accompaniments using some neat instruments called "Smart Instruments" . Just enter the chords you would need. Record the chord progressions on the Smart Instruments(Piano, Bass, Strings and Guitar)with the variation(4 variations per smart instrument) and voila.. you have an accompaniment track that behaves just like a song`s backing band.

And talking of songs I just added one more. Check it out
Where have all the flowers gone ?

Wish you a great weekend !!