I'm hoping Jerry's doing this just to humiliate Howard. Revenge for all the hours of radio time Howard's filled by replaying bits from 20 years ago: Shoshanna Lonstein song parodies, Gilbert bombing his answering machine, etc. I can guarantee Howard's going into this knowing he doesn't stand a chance if he tries to do anything other than his complaining schtick.
Really, this may be the best thing ever. I can not fathom how poorly Howard will come off. The only thing he ever does on Letterman, etc. is bully and try to take over interview. That is NOT what Seinfelds show is about. I can't wait.