Doesn't take much.
For the moment I am using a MacBook Air, PreSonus AudioBox 22vsl, Logic Pro 9, and Toontrack Superior for my drum stuff. This of course is meant be use as a portable studio so I can travel and record, but I am doing some decent demo stuff right now.
Going to get a stationary set ups as well, but right now, this is good for me. Besides that, I can record demos, work on the arrangements, get all of my preproduction out of the way to cut down on studio time. I'm only interested in going into the studio to record live drums. I can do all the other stuff else where. Get all that mixed digitally, then take it back to the studio and slam it hard to tape. Its going to work for me.
Cheers!