i disagree that logic is overkill. it can do very basic stuff to very detailed stuff. garageband is too basic and doesn't allow you to bounce tracks without going thru itunes, no editing, etc.
just take your time and start with an apple drum loop to keep your timing. then record over and over until you get it right, no matter whether it is a one minute song or a 10 minute song.
make sure to check the apple discussion forum for logic. a wealth of info there and people who have already gone thru what you are now doing.
here is the link to the logic forum:
https://discussions.apple.com/commun...categoryID=231
here is sf ninja and tons of his tutorials on logic:
http://www.youtube.com/results?searc...be.kBx0OYIGLQA
and, here is a google search of david nahmani's apple logic certification book if you would prefer a book. it is very well organized and walks you thru recording while you apply the information. david runs the logicprohelp forum which you should join also.
https://www.google.com/search?q=logi...=1804&bih=1058
play music!