I just had to complete a stair climbing challenge for RPI's Intro to Engineering Design class. Here's what my team learned with a tracked Vex robot.
The key to going up - and down - stairs with a tracked system is CG. Your left-right CG should be centered so that you track as straight as possible. You will want to move your CG around going up and down steps, however. If your tracks span more than one step, you'll want your CG more forward than aft. On the way down, you'll want it more aft than forward to prevent rolling right down the stairs. Of course, with all CG problems lower is always better, and a low CG means you have to displace your CG less.
The other tricky part of stairs can be climbing the vertical face of the step (the "first step problem"). With enough traction, you can "roll" up the side of the stairs, and if you lack the traction you'll need to find other means to "pop up"...
