Coming back into the mix. Obviously this is still hotly contested, and there's no real "right" interpretation of the Amendment (except applicable judicial cases, where it is legally interpreted in a court of law.)
In my base opinion, "well regulated" isn't something of hard form, with rigid restrictions, but rather something that performs well and runs smoothly. This is interpreted many ways because language has changed a lot since the Bill of Rights.
"Militia", again in my opinion, refers to citizens that are of military age, acting as more of a reserve force for the military than anything else. Now, here is another place that is contentious, because of the fact that the Militia is not well-defined in this instance. In the historical context, militias were citizen fighting forces in the original 13 Colonies. But some militias differed greatly from others in terms of setup, and the world "Militia" itself was used to refer to armed citizens that could be used for fighting, and not actively in duty. Sooooo, it boils down to whatever you want, because the legal interpretation is left to the people who are supposed to interpret the laws to the best ability possible.
Now, if you want the LEGAL interpretations, read District of Colombia v. Heller, which talks about the Supreme Court ruling on individual rights with guns, and Caetano v. Massachusetts, which rules on what guns are allowed under the Second Amendment. I would also recommend reading the briefs on District of Colombia v. Heller to get a sense of the amount of information that the Supreme Court handles before making a decision.