Firstly; I know most people are instantly thinking "gah, another n00b not posting in the sticky we built", however I felt that with so many people worrying over whether their £500 builds will even run the game it would be good to share my experience from the demo.
Secondly; I do not have the full version yet, I have been running the demo - however I doubt there will be any major difference in quality between the retail and the demo.
Thirdly: I know many people will upgrade anyway, just to get the difference between high and v. high graphics - I'm not trying to put them off in anyway, just showing people that they probably won't need a brand new PC to run it on good graphics settings.
Anyway, so before arma2's release and the couple of days after it (german release) all I saw was people with extremely high end PC's - either quad core or overclocked dual cores running the game, often not even on the highest settings. This alongside the minimum system requirements made me feel like a new PC build would be needed (Note: I've had this PC since ~2001) possibly costing in excess of £500. Now I know there's tons of people asking also "will my PC run this" and giving a full list of their dual core system settings; all I have to say is "yes", maybe not on full but "yes".
To cut to the chase, I have been managing to run on 30+ FPS (more than I need to be happy) with all settings on normal (except object detail and post production, which are on high) at 1024x768 (yes I know it's a low res for you guys, but it's better than having high-res and jaggy objects). All of this, with a good number of units on the screen at once and multiple explosions etc (the general wartime stuff you get in arma2). So the "rig" I've been using to achieve this:
Memory (RAM): 2048 MB
CPU : Intel® Pentium® 4 CPU 3.06GHz
Sound card: Realtek HD Audio rear output
Display Adapters: Radeon X1950 Series
Hard Disks: 260Gb (stock HDD)
Motherboard: ASUSTeK Computer INC. Puffer2
And yes that is the Intel Pentium 4, Single core, from Nov 2000 not overclocked. The graphics card a lot of you will recognise is also DX9. So if you had any worries about whether your intel Q6600 with ati HD4870 will run the game - I hope this has helped squash them.
PS: I Don't mind if you move this if you feel it'll make less clutter on the main page.