After a very long time of trying to convince my friends to get ARMA2, they finally have. My friends had read that the official campaign for ARMA 2 can be played coop, and that is what they want. I am not sure if Harvest Red supports 5 player coop, and if it doesn't I need a campaign that is.

What campaigns out there are coop for up to five players? (yes i have used search)
If I edited the Official campaign to add more slots, would it break the campaign worse (if its even editable)
Are there a series of good missions that could stand in as a campaign

No, the stock ArmA2 campaign "Harvest Red" only supports a maximum of 4 players in Co-Op. If you want to play campaigns in Co-Op with at least 5 players here are my sugestions (I'm assuming that you and your friends have ArmA2:CO or ArmA2+OA):

- Joint Operations, a campaign that uses BAF official DLC (British Units) and IMO it's the best user made campaign made for ArmA2 so far (at least regarding the ones that I tried so far) and it can be player with up to 8 players in Co-Op. This campaign can be downloaded here:
Joint Operations

- Delta Force 1, a campaign that uses Lingor Island and Lingor units addons and can be played with up to 8 player in Co-op (if I'm not mistaken). This campaign is based on the old Delta Force games from Novalogic. This campaign can be downloaded here:
Delta Force 1

- Delta Force 2, a campaign that uses no addons and can be player with up to 8 players in Co-op (if I'm not mistaken) and is somehow a follow up from the previous Delta 1 campaign. This campaign is based on the old Delta Force games from Novalogic. This campaign can be downloaded here:
Delta Force 2

- Ghost Recon: Island Thunder, a campaign that uses Lingor island and Lingor units addons and can be played with up to 9 players in co-op (if I'm not mistaken). Like the name says, this campaign is based on the Island Thunder addon for Ghost Recon 1. It can be downloaded here:
Ghost Recon: Island Thunder


I hope this helps and keeps you and your friends "occupied" for a while

Thank you for your reply, Those will help a lot.
My friends purchased Combined ops from Steam while it was on sale. I hope this keeps up busy, but we will see. Tonight will be the first time they have tried ARMA2, they may hate it.

I just wanted to post again so I can write down my experience. The game sessions so far haven’t been bad. The first game night was filled with

What is the jump key?
Where is the enemy?
How do you get into Vehicles?
Who killed me?
Did I just kill you again?
How freaking big are these maps?
etc.

After the first night we went in and played some of the official SP missions I converted to MP (they all worked fine) still my players did things like.

Drive full speed into a town and try and run over the bad guys.
Rambo charge and wonder why they died
Stand in the open and look for the enemy and died

That was all things they will learn not to do in time, and it was getting better near the end of the second night.

I just knew they were going to complain and say “this game sucks” or “this is too hard and not for me”, but they didn’t. The one complaint they had was the end of the missions were anti climactic, and that a simple score board will kills listed seemed like a letdown after a long mission. On that note I would like to pose a question to the community.

What would you like to see at the end of a successful mission to make it feel exciting, and that you had done a good job?

My initial thoughts were for a failed mission an OUTRO with a set number of graves, flag flying in the background at sunset

For successful completion, an OUTRO with a podium like scene with the top 3 scorers standing on the podium (is that even possible?)

I always expect lots of explosions and fireworks when I win something...

@HellfireRWS:

I think your friends are still very Call of Duty or Counter Strike "formated", if you know what I mean. With this what I also mean is that how you play an arcade game like CoD or CS and a realistic game like ArmA are basically opposed! While with CoD the main objective seems to be the player who kills the most or to kill as many as possible before dying (specially in Multiplayer) and avoiding to be killed in CoD or CS seems to be a very secondary objective while with ArmA the main objective is avoiding to be killed and completing the objectives as a team while killing enemies is actually quite secondary just like in real life (not that I've been in any actual war - "thanks god" for that - but I can easily imagine that this is what happens in a real war) hence why ArmA is considered a "realistic game".

IMO the best way to be immersed into ArmA is just pretending that it's just like real life and in real life you definitly don't want to be killed therefore you should move carefully like using every possible cover (houses, rock, trees, etc...), NEVER ACT LIKE RAMBO and acting like team - if you move an engage the enemy alone (again like RAMBO), you're dead (just like in real life) - but if you engage the same enemy as a team your chances to win and to eventually kill enemy soldiers are much higher! The use of proper tactics are also very important to win in ArmA - for example a weapon that I never used much in other tactical shooters (like Ghost Recon 1 or Rainbow six) were the Machine guns (like the M249 SAW, M240, PK, etc...) but in ArmA I learned to LOVE these weapons a lot and with my friends using assault rifles or even sniper/marksman rifles I learned that using Machine Guns together with my friends that our squad had a much better chance to be sucessfull since a machine gun gives a tremedous firepower boost to the squad compared with any other gun (assault rifles or sniper rifles for example) and effectivelly supresses the enemy (even AIs) which works very well in ArmA!
Another advise that I can give to your friends is that each of them could "specialize" with into a diferent kind of weapon/role like for example one as a grenadier (with grenade launcher), another as Anti-tank specialist, another as sniper or marksman, another as machinegunner and so on...

Regading OUTROS or INTROS, yes there's no doubt that a very good or excelent INTRO and/or OUTRO gives the players a much bigger immersiveness but the "problem" is that a very good or excelent INTRO or OUTRO is very time consuming and hard to do (probably as hard if sometimes not more than the mission itself) and some missions actually have INTROS and OUTROS - The existance of an INTRO or OUTRO in a mission is only dependent on the person that makes the mission.
And from my personaly experience with ArmA (which pre-dates from OFP-CWC) is that a bad, mediocre or even an average INTRO or OUTRO isn't immersive at all. Actually IMO, it's preferable NOT to have any INTROS or OUTROS than have a a bad, mediocre or even an average INTRO or OUTRO in a mission!