How exactly do you see Colin Powell (Republican with an aggressive, if considerate, foreign policy) matching up with Barack Obama (Democrat, with a lenient foreign policy)?
A lot of their opinions differ greatly. Colin Powell is very conservative (though this might be tainted by the fact he is/was surrounded by neoconservatives). Obama is very liberal. It'd be like the odd couple. They'd argue all the time and get nothing done. Not that Colin Powell didn't do that at Secretary of State :P
Even the thing that would make a telling exception to the above - that Obama really wants to allow surgical strikes against Pakistani terrorist targets regardless of Musharif's cooperation - sounds exactly like something Colin Powell would OBJECT to. The guy had it right when he said invading Iraq was a mistake. The only reason he became a huge front for the bull shit that followed is because Bush forced him into the position of 'Head of Military Propoganda'.
Overall, I've got no problems with Colin Powell's excellent military expertise being used but imho, he wouldn't make a good advisor on much else and probably a bad vice president when the US wants to be aiming at withdrawls over invasions. And there just isn't a way he'd synergise with Obama in anything other than a military position.
Yhorian