The basic rule of Canadian politics is so simple that George Bush understands it: Either you're with me or you're against me. So it's no surprise that Liberals - having had their government (temporarily) rescued by a deal with the NDP last year - are now screaming bloody murder that Layton would dare do the same thing again. You see, it's only acceptable for the NDP to work with a minority government if it's a Liberal minority, apparently.
Equally clear is that all the Conservatives who screamed bloody murder for the Liberal-NDP deal last year will now praise Harper for his willingness to compromise, and they may even (!) spare a kind word for the NDP - though I'm not holding my breath.
Let's cut the bullshit. The Liberals are not going to force an election anytime soon - given some conversations I've had, I'm beginning to think 2008 is a more likely time for a trip to the polls. If the Libs won't force an election, the NDP and the Bloc can't. That only leaves Harper the opportunity of committing seppukku for reasons of his own, but I doubt that will happen either.
So we're stuck with this government for a while. That leaves Layton and the NDP two goals: be seen to minimize the damage Harper can do, and make the Liberals look as bad as possible. This two goals are the basic strategy for Layton's goal - shocking, for a politician - of increasing his political relevancy.
Working with the government serves both these interests - try and fix the otherwise-crappy clean air act as much as possible, and cut the Liberals out of the process as much as possible.
Liberals don't seem to understand how bad their situation is: every single party in Parliament is trying not just to defeat the Liberals, but to try and eliminate them as electoral competitors for the foreseeable future. Moves like this - if Layton manages to pull it off - are risky, but smart.