I also needed to do this for my own recording. I've been ask a number of times how I make drum parts so I typed up a "how-to" for creating drum parts using pre-recorded loops and sequencing software. In this case, I used Acid. To my understanding, Acid Express is available at no charge and can easily do this. You can see this here:
http://www.darenwoodall.com/misc.htm
This is a really effective option that many don't consider.
If you are not as concerned about the sound quality or "natural" sound of a real drummer, there are lots of free drum machine software applications you can find with a Internet search.
Daren