Hi SEgunner,
It totally depends on how much money you want to spend. Reasonable for the computer system (only the box with what is inside, mouse (20$)+keyboard (20-100$)+display(200-1000$) goes extra).
Cheapest system to get AH2 at full specs runs for around 900$, most expensive system that makes sense to buy is at about 1900$ but you can get it more expensive if you want to have the most exotic... but gaining little there for home use in my opinion.
Something like Athlon64 3700, Nvidia 7600GT (the GT is important), 2 GB Ram, 120GB Harddisk, Brand motherboard and powersupply will get you good performance in ah2, but certainly is far away from a top framerate monster for other games. Most run good but you can have better. That is probably what you get for around 900-1000 Dollars.
Best performance for reasonable money in my opinion currently would be getting a conroe 6600, 2GB DDR2 RAM, Quality 200GB harddrive, Nvidia 7950GT and a good soundcard, but that will set you at about 1500$.
Best high end I would usually take whichever processor is fastest in the second most expensive group... So while the high end processors are at 1000$ youll get one 10 percent slower for about 600$. So i would build around that.
Of course add DVD writer, case, powersupply, floppy drive, fans, fancy lights, stickers etc.
1.) Choose which price range
2.) Choose which processor fits there
3.) Build around that
4.) See which extras you need (Second disk, 3 more disks for raid, high quality sound etc.)
5.) check if the selected motherboard supports all that and still is the best choice
6.) start at 2 if again if you dont like the final price
