Will you be able to scavenge the computer you are currently using for parts, or is it going to be given to someone else?
If you can scavenge your current rig, I suggest you post all of it's components' specs here... Some parts you certainly have to replace (motherboard) but others you may be able to carry over (case, power supply, RAM, DVD/CD drive, hard drives...).
I think Perfesser's comment:
For myself, to leave room for upgrades, I used the lower end PC package with the exception of the power supply and motherboard from the next higher package.
That was 2 years ago. I could now buy the faster 3.0 chip (at half the price it was then) to replace my 2.66, stick in a bit more RAM and perhaps a better vid card (all simple plug-ins since the basics are already there) and have a considerably upgraded system.
Is very good advice- buying a decent, but not bleeding edge ($$$) machine, that can be upgraded over time will give you the option of installing better vid card, CPU etc...
A good start would be an intel E8400 (for the games you are into which you can overclock. In my view there is no point in going to four cores for you, IL2, FS9 [and I believe BF2] do not implement multi-cores. Dual core will do you fine, and any mobo for a dual core should be good for a quadcore when the prices of those come down. The intel i7 chip will need a new Mobo- but I don't think you can afford an i7 rig at the moment.
I haven't been following the tech for about a year and a half (when I purchased my present rig), so I may be wrong about the details of the above.