What is a Well Regulated Militia?

The 2nd Amendment:

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.

Ok, so what exactly is a "well regulated militia"?  Is a militia now what we consider the National Guard?  Is it the entire pool of eligible citizens that could be called upon at a moment's notice ?  Or is the 2nd Amendment simply intended to grant individuals with the right to bear arms?  If it is the latter, what makes these individuals "well regulated"? 

I guess my basic question boils down to this.  Is the 2nd Amendment intended to ensure individuals the right to bear arms, or is it more of a question of state's rights to ensure that (well regulated) militias have the right to bear arms to protect the security of a free state?

Btw, one of the more asinine things I've heard about gun control laws came from Neal Boortz.  He argued that gun control laws would simply make it more difficult for law-abiding people to get guns, and not the criminals.  Boortz disregards the fact that Seung-hui Cho was law-abiding when he bought his guns.

Chris