Flight Sim Build

I am an avid flight sim player, currently playing IL2 on an 8 year old Dell that has served me very well. Now I want to build a butt kicking system that can not only handle IL2 with full graphic settings, but will also easily tackle Rise Of Flight at full graphic settings. Here are Rise Of Flight min system requirements from their site:
Operating System: Windows® XP / Vista
CPU: Intel® Core™2 Duo 2.4 GHz
RAM: 2 Gb
Internet Connection: 256 Kb/s (required)
Graphics Card: 512 Mb, GeForce 8800GT/Radeon HD3500
Sound Card: DirectX 9.0c compatible

I figure if those are the minimum requirements, then I should probably try to double the performance of what is listed. My goal is to be able to build a system that will last a minimum of 5 years and easily upgradable. I'll need a case as well. I'm very interested in using an Nvidia card as opposed to an ATi, based on recommendations from the IL2 forum and other flight sim forums.

The only caveat to the whole thing is that I'd like to spend about $700 to $800, realistic or no?

I haven't ever built my own system from scratch before, but I have upgraded and previous ones extensively, so I know enough to get into trouble!

Thanks for any and all advice and suggestions!