We're really only assholes to kidiots who won't listen and to the odd 18+ person who types in "txt sp33k" (god that peeves me off).
Anyways, mechbox.com has videos of the takedown but as for detailing the differences I don't know of any site that does a through job of it. All you really need to know though is that V1 is hard to find parts for and is used in the FAMAS, V2 and V3 are common, V4 and V5 aren't that common but one of them is used in the Thompson and possibly the MP40 or something, V6 is used in the P90 and Aug, and V7 in the M14.
The major differences are shape to be able to fit into certain bodies but there are also some design improvements. Worry about the V2 and V3 for now. With the V3 there are some improvements over the V2 system what make it more suited to cold weather (it's still not recommended to take it out into cold weather or parts might break from cold stress), as well with the V2 there's some problem with shock to the mechbox shell or something that the "V2fix
" fixes by absorbing the shock or something.