maybe a short brief before it starts? Go over basics and what not?

I haven't played Arma II, just heard it was considerably different than most shooters. I'm still assuming their are maps to learn and you gotta figure what weapons do what. Homefield advantage is a mother-blam!-er to overcome. I'd still predict the veterans hand out an asswhooping.

It can be, and at times it is. It is a lot slower paced. Firefights tend to happen between 100 and 300 meters, just like in reality. If you are doing CQB you are either room clearing, Special forces, or doing it wrong. A decent shooter can hold off a squad or even a platoon if they have bad situational awareness. Learning the map isn't so bad, especially if you have experience reading topographical maps. You open it up, see where you are, and bam you know where you are. Some weapons do perform differently. It depends on Caliber. a .308 will hit a lot harder than 5.56 and so forth. If you use suppressed ammunition you are at a huge disadvantage in ranged firefights. Made the mistake once of taking a suppressed UMP .45 on a mission. Got into a engagement at 100 meters, got -blam!-ed. To be perfectly fair, just about any small force with capable members and a capable commander will hold their own in a defensive battle against a larger force. Some times Numerical advantage is a disadvantage. Though this is more of an experiment of how fast they can react and return fire. How fast they can organize and move out of the kill box or even assault our positions. Like I said, they will have AI CAS at hand if they need it. the M2 on a HMMWV is good out to 2 clicks, and devastating under 1.

I think the part where it would really fall to pieces is hinged on the word "organize." In my experience with online shooters, that isn't typically a strong point of most gamers.