Layne,
All of the tests you're interested with a 2x2 repeated-measures (or within-subject) ANOVA can be obtained with 3dMEMA or 3dttest. For the contrast of (a1-a2)_b1 and (a1-a2)_b2, you just need to collect (a1-a2)_b1 and (a1-a2)_b2 from each individual subject, and then run a paired type test with 3dMEMA or 3dttest.
Gang