Be carefull id be afriad to put anything on the trackpad because it is quite delacate. See if just a little water would do the trick first. YOu never know how some marterials and substances will react to one another.
If you are not sure, try using your towel that you used to dry yourself after a shower (or a moist towel) . At least that's what I did for my white ibook that attracts dirt.