Like I said before, the 2nd amendment applies to militias, and the people that make up the militia.
The Militia refered to is, as mentioned afore, all able bodied persons of adult age (back then it was men 17-45), now generally taken as any US citizen of legal age.
The National Guard takes it's roots from the "Militia's" of old but was really designed as a first responder to a need for soldiers(ie indian attacks, darn those redskin brothers of mine
) till the regular militia's could be formed. "The Patriot" is a good example of what I mean, the movie compresses it, but you see how Militia's of old were "activated," by a rider going from town to town, house to house looking for the able bodied. After the revolutionary war, many states (and the Federal Goverment) decided that they should keep some soldiers trained and offer training to the "Militia" so that they could rapidly field an army, instead of the months long process normally needed to gather, train, equip, and then deploy a normal "Militia." Their creation lives on today as the Army and Air National Guard, each controled and governed by the state they reside in, unless "federalized" by presidental order (as the boys in Iraq, an else where on Active Duty have been) This is why you see the National Guard being the called in for floods, and such in their own states typically, as Az guardsmen have no authority in CA, and vis versa.
So to summorize, the National Guard is actually the historic "Army Reserve" who is Citizens who have been trained to Active army standards but aren't actual (federal) military soldiers till activated. Where the Militia is all able bodied indivuals who could be "Drafted" if the draft was re-enacted.
Good case in point about the NG and our military (you might want to fill in the blanks) but there was a standoff back in the 60s where the NG and military had guns pointed at each other...I remember it was over race but cant recall the state That was in Alabama if memory serves me correct, but I am certine it was one of the southern "segregated" states. The State was ordered to end segregation at a school (college I believe) and was asked to use the National Guard to help enforce the desegragation, and prevent harm happening to the "black" students that would start attending. The Governor though was a "good ol boy" who used the Guard to keep the students from attending, and the Federal government was required to send Active duty troops from elsewhere in to handle the security. And from what I've heard it wasn't guns pointed at each other, but a VERY strong and heated argument over who's turf it was, and who was gonna stay, and both sides were armed, with weapons and live ammo. (this was before they got too scared and PC to issue live ammo to troops, like now days for riot control ie florida in the late 90's)