1) The War was Just and a "Good Idea" That is to say, it satisfies their definition of a just conflict, and so rightfully done, and furthermore not only just but a good idea either strategically, on humanitarian grounds, or just in our best selfish interest. This grouping I think defines most of the Iraq War supporters.
2) The War was Unjust but a "Good Idea" That is to say even though we didn't have a good enough reason to enter into to the conflict, we had so much to gain by entering into say either lots of oil or spreading oil on the troubled waters of the Middle East conflict that it made sense in a "realpolitik" fashion to do it anyhow. This group I think is probably small.
3) The War was Just but a "Bad Idea" While meeting one's criteria for Just War, many possible conflicts might fill that bill. For example, one might advocate jumping into the fray in the Sudan right now. But, while the Iraq endeavor might have been just, it was unwise. Perhaps too expensive, too difficult, or a bad strategic choice.
4) The War was UnJust and a "Bad Idea" This group defines (I think) most of the rabid anti-POTUS denizen of the left.
A few observations. Number one, I don't think "4" is necessarily only amongst rabid-leftwingers. Republican isolationists would probably fall in this camp too. Moreover, people who think that the US needs to be bound tightly by international law and needs to be restrained by international institutions could easily be here. Some of those people are kool-aid lefties, but not all.
Now, what about me? I'm not a huge fan of categories in general--they always seem to paper over important complexities. For example, I probably am a "1," I think the war was "just" (on humanitarian grounds) and a good idea (democratization aids the war on terror). I also think, however, that it was remarkably poorly executed. If I had known that the Bush administration would conduct the war in the manner in which it did, I'd be far more uncertain about the war being a good idea. Also, there is the question of opportunity costs--if intervening in Iraq means that we won't intervene in Darfur, then whether or not it was a "good" idea becomes even more muddy.
I think that there is another permutation that has to be added to the categories: "done right" versus "done wrong." I'd be a "Just war, good idea, done wrong" person, as would, for example, Andrew Sullivan. The most pro-war republicans would be "just war, good idea, done right." The most partisan leftists would be "unjust war, bad idea, done wrong," while I'd suspect you might find a reasonable amount of Republican isolationists in the "unjust war, bad idea, done right." The other categories would probably have smaller mixes.
Just my two cents.