I have a feeling that if Overture was going to come up with a 'contextual ppc thing' like Adsense they would have done so by now. Unfortunately, there's a rumor going around that they won't be opening up such a program anytime soon--their back-end system(s) can't support it.
They do have a system they just only deal with high traffic sites and make them sign a very restrictive contract. From what I hear it is the best if you can get it. It is supposed to pay a lot better than adsense.