Some additional background on the Second Amendment can be found here,here and here.
UPDATE: Okay, I've given the majority opinion a very quick read. It's very much in line with the so-called "Standard Model" of individual rights scholarship, and also makes much of the Tennessee cases that I discuss here and that the Supreme Court noted in Miller. Seems like a very strong opinion; the dissent, on the other hand, looks a bit odd. I'm going to have to think about it a bit more to decide if it's really as flimsy as it seems.
ANOTHER UPDATE: Eugene Volokh notes the decision, and has some further thoughts about timing and the 2008 elections.
Perhaps the Democrats would be wise to take the issue off the table politically by passing some sort of federal legislation guaranteeing American citizens the right to own guns.