Smitty's first post and Bob Schwarer's last post conform to the principle I've heard that the "well regulated milita" potentially consists of every citizen. Although the National Guard is sometimes called the Militia, it is not the same thing. It is instead essentially an auxiliary branch of the U.S. Army. The citizen milita mentioned in the 2nd amendment is not a regular, organized, ongoing body--it is everyday folks equipped to fight tyranny if and when necessary. Note that the amendment does not say that one must be an official member of the militia in order to claim the right to bear arms, it merely mentions that a free state needs the capability to have one--in other words, the citizens must be capable of effectively resisting an oppressive government. The fact that U.S. citizens have as yet not needed to do this attests to the good design of the Constitution as a whole, but does not render impossible the need to do so in the future (I don't think it will ever happen, but it's not impossible).

This right does not extend to doing whatever one wishes whenever and wherever ones wishes with his weapons, thus the various laws restricting and regulating the possession and use of arms. But the basic right to own them was, and by many still is, considered essential to prevent, and if necessary depose, an oppressive, tyrannical government.