Hi,
Was just reading these forums and thought I should join up and give you my experience... I have a late 2009 iMac 27" with the i5 processor (I believe) and just recently bought ArmA2 OA over steam to play.
I run windows 7 through bootcamp, and I can assure you that it runs exactly as a 'normal' PC (there really is no 'special' Mac hardware or anything, it's just a computer). You will get a disk that has bootcamp drivers on it, simple as running bootcamp in OS X, installing windows, then popping in the bootcamp disk when prompted.
Now to ArmA2... it runs.. Ok, My iMac is fairly old now so I expect you would experience quite a performance boost with a brand new 2011 one, but there's no way you would be able run it in the 27" native resolution (I can run it at 1920x1080 but texture etc must be on low).
I was actually very surprised how well it ran, it could be better but I just enjoy flying choppers and blowing stuff up occasionally!
On a side note, you can download Steam for Mac, and they are Starting to publish a lot more games on both platforms..
Hope I was some help! :)
