Yep. It is a good idea.
Some quick fire answers.
Epic Armageddon was the last version of an epic game gw put out before pulling the pin. It is continuing to develop in the form of Net Epic Armageddon. The rules don't seem to change much (with faq's being the most frequent update), but the army lists are quite specific and get a lot of development. It is most widely used for tournaments and has the most community involvement.
As well as the TacCmd forum Epic Armageddon, check out this site for the latest rule set and approved army lists:
http://www.tp.net-armageddon.org. There are a lot more lists being developed in the NetEA army list compendium as well as in sub forums.
Epic 40k was the previous version. I don't know much about its current status to be honest.
Before that was Space Marine (or Epic), which is continuing to be developed here. The rules are being developed, and are up to version 5, with version 6 currently being fleshed out, but still a way off. NetEpic Gold is basically the v5 rules and army lists with fantastic miniature photos in it. As well as the NetEpic section of the TacCmd forum, this site has the downloads needed to play:
http://www.netepic.orgThe three versions of the rules (and their army lists) are incompatible.
Epic Armageddon plays quicker, but has less detail. It was created around the time of 40k 4th edition so you can see some instances of units in it that fit that time, but have since been updated by gw in 40k (eg scouts have rhinos, not land speeder storms which weren't invented then).
NetEpic has more detail, but more book-keeping. It also has more "legacy" units and formations that don't fit the current 40k fluff, that gw have continued to refine eg IG predators, terminators in rhinos etc).
I believe Epic 40k is somewhere in between.
Hope this helps. Apologies for the wall of text.
