Arma2 is VERY CPU intensive, recommended specs for the game suggest a quad core Intel @ 2.8GHz. Even the best machines struggle with it so getting any laptop to play it would difficult anyways. With the last gen core i3 and the 540M it will be pretty sluggish.
Here are some benchmarks for the GTX 540M
http://www.notebookcheck.net/NVIDIA-...M.41715.0.html
Most games are playable (30+ fps) on low or med with the card and the test setup. Med2 should be no problem. I can play Med2 on highest settings on my Core 2 Duo with a 9800GTM.