I actually think that the two are related. If Boehner tries to lead a defunding fight and shuts down the government in the course of that fight, and then loses the fight, a drive for impeachment may come as a reaction to that failure. In other words, I think the Republicans may really take the criminalization of political differences to new heights --they'll try to impeach Obama precisely because he passed the health care law and because he fought off efforts to defund it. Why the hell not? The phrase "high crimes and misdemeanors" sounds so vague to modern ears, and voices of reason are in such short supply (and such low regard) in America, that Republicans could try to impeach Obama over anything plausibly. So if they lose a defunding/shutdown fight, they'll just fight to defund on another battlefield. And it will all be deemed Obama's fault.
That's certainly plausible, but again that's assuming there's still any sort of logical progression in the GOP leadership post November 2010, which I'm saying there will not be. There's a very good chance you will see the Republicans go nuts and attack the President and his policies from every angle: defunding his programs, forcing a shutdown, and leading impeachment investigations, and doing it all at the same time.
Steve is right however about all of it being Obama's fault. That's being set up now. No matter what actually happens in November, Republicans "won a mandate" and Democrats "need to listen to the people."
Exquisite chaos approaches.