Well, let's see.
A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.
It seems to clearly state that United State's citizens have the right to bear arms, and that right shall not be infringed.
According to thefreedictionary.com, Arms: 1. A weapon, especially a firearm.
So, by definition, United States citizens have the right to own guns, and that right cannot be taken away.
So, on to what this thread is actually about.
I've seen most of the anti-gun points in this thread too many times, and the logic behind them is lacking.
Let's start with personal firearms for protection, and work our way up to the whole militia ordeal.
My hometown has somewhat-active gang activity in the less-than-desireable areas. Yes, there are a few gun crimes, and just about all of those involve someone breaking into someones house and shooting them, shooting someone over a car, or shooting someone for no reason.
Not once have I read of these incidents in which the victims were carrying firearms, bsides gang shooting each other.
However, there are also multiple incidents of armed citizens scaring the bajeezus out of a would be robber, even though sometimes the robbers were armed themselves. One account for example:
2 local gang members showed up at a man's house (the reasons for this were not disclosed by the police department), and threatened to shoot him. He, in turn, went and grabbed an assault rifle (which he had the necessary permits to own) from his closet, and told them if they came in his house, he would shoot them both. They broke in his front door, and he fired on them. One was killed instantly, the other tried to run away, shooting as he ran, and later died at the hospital. The homeowner was unharmed.
I've had friends have knives pulled on them in robbery attempts, only to flash a concealed handgun, and have the idiot robber run scared.
I know crime rates are not the same in every area, but given the time it takes a police officer to respond to an incident, guns invariably protect people as a first line of defense.
Now, on to the militia point.
Yes, an assault rifle will not do much to, say, an M1A1 Abrams. A shell of 12 guage buckshot will just piss off a humvee driver. Regular firearms won't do much to stop a well regulated military.
I've recently been studying up in the old military handbook for guerilla warfare tactics, troop placement, rigging and other...things.
If anyone has ever paid attention to the news, you will notice that the US has been supplying rebel faction in other countries with weapons for years, and they have overthrown armies without United States military intervention.
I saw a post a few pages back about IED's being heavy and bulky.
I can make "something" that will burn through depleted uranium and steel plate armor in 15 seconds flat, and is about the size of a notebook binder. I can rig a rather destructive item from a model rocket and other things that don't need to be mentioned.

There are ways for civilians to stand against an organized military, but they themselves must be organized.
An organized militia. With soldiers, people gathering intel, pilots, engineers, and all of them happily smiling and in the same clothes as Plain Joe over there.
It wouldn't be easy to oppose a military force, but it could be done with time, the right minds, and in secrecy.
One point that I haven't seen, but I may have missed, is the assumption that all military and police personnell would stand against the civilians in a government vs the people war.