Of course an armed populace could resist a trained military ... unless that trained military simply wanted to exterminate everyone else and was willing to use massive firepower or weapons of mass destruction to do it. Not win outright, but resist, hopefully long enough for the forces of oppression to come apart at the seams.
Would Canada and Mexico become the resistance's Pakistan?
Then there are always scenarios with foreign invaders, alien (ET) invaders, mutant giant spiders, genetically engineered dinosaurs, or zombies.
By the way the SCOTUS heard another gun law-related case Nov 10th, U.S. v. Hayes. The focus is on interpretation of the Lautenberg Amendment to the Gun Control Act of 1968. The decision should be interesting.
Oral arguments: http://www.supremecourtus.gov/oral_arguments/argument_transcripts/07-608.pdf
Briefs:
http://www.abanet.org/publiced/preview/briefs/nov08.shtml
EDIT: Trying to fix the first link.
Edited, Nov 12th 2008 12:05pm by Ahkuraj