I use EZ Drummer as a plugin in Garageband. Like it says above, you can set a drum loop to play endlessly until you "find the pocket." Once you're ready to demo something, put your various loops in order and play right through it. No one is expecting a non-drummer to be a programming genius - usually the strength of a song will shine right through.
Basslines tho? Oh man, I almost think it's worth learning bass just so I can get some bottom in there!