See my post 82. The 22nd Am. does not prohibit a two-term president from serving as president, only from being elected president again. The language is pretty clear.
If a two-term president was deemed (through judicial activism) to be ineligible to serve as president again, then, under the 12th Amendment, he would be ineligible to serve as VP.
I read the 22nd as preventing a person from serving more than 10 years as President. One interesting test would be if, say, Bubba Clinton (or Dubya, for that matter) decided to serve as VP to whomever, and that person is forced out after, say, a year, meaning three years left on the term (and the 22nd explicitly says shall not serve longer than two years of a term to which someone else was elected). Would he then be compelled to step down precisely at that two year mark in favor of their appointed VP, or allowed to serve out all three years ?