I can reccomend you to be sure to get a SSD (Solid State Hard Drive- a very fast hard drive) and lots of RAM (6 GB at least, 8 is even better) if Arma 2 is what you are after.
For more details about Arma 2 being bottlenecked by the hard drive speed and the ways to counter it:
http://forums.bistudio.com/showthread.php?t=88388
As for the rest, if you don't have a relative or friend that can help you, just go to a good PC retailer, tell them what is your budget and have them offer you 2 or 3 options. Put the options here and then we could reccomend the best one for you.
For more details about Arma 2 being bottlenecked by the hard drive speed and the ways to counter it:
http://forums.bistudio.com/showthread.php?t=88388
As for the rest, if you don't have a relative or friend that can help you, just go to a good PC retailer, tell them what is your budget and have them offer you 2 or 3 options. Put the options here and then we could reccomend the best one for you.
The fewer men, the greater share of honor