Hydrogen is an incredible open source drum machine program. It comes with a bunch of kits and you can download more. I used the windows installer to run it on XP and it works great.
Hydrogen - advanced drum machine for GNU/Linux
Once you have your drum track you can save it as an MP3 and then bring it into Reaper. Reaper is not really open source or free but it is a professional level recording studio that is fully functional without registering it. If you don't register it you just get a notice each time you start it. If you are registering it for home use it's only $50. It's $225 for commercial users.
http://www.cockos.com/reaper/