I can give you a build that i...built, for about that range.
You can probably get it for lesser though, seeing as things cost moar here.
Cpu and motherboard combo (they come together) cpu: AMD Phenom II X2 550BE (3.1GHz) and motherboard:ECS A785GM-M, together they cost = about $180
Memory: Get any memory but make sure that it does not come below 800MHz (each), i would suggest 3 or 4 Corsair/G.Skill 1333MHz DDR3 ram, this will cost you about $27 X (the number of memory cards you buy), two will be fine also but you should get 3 at least, price differs from company to company so get the best deal you can.
Graphics Card: Ati radeon Sapphire HD5750 1GB: $180, you can even buy XFX instead of Sapphire, same card, but XFX gives better warranty, however, it will probably be costlier.
Hard Drive: Seagate Barracuda 500 GB: $50, this is what i suggest but you can buy whatever you want, that is up to you.
Cabinet: CoolerMaster Elite 310: $32
Power Supply: Gigabyte Superb GE-R460-V1: $44
Optical drive: DVD Writer: $22
Moniter: Again, up to you but i would suggest you buy the BenQ G2220HD (22" Full HD), I really don't feel the need to have hunormous monitors clogging up my table: $156
Keyboard and mouse: Buy anything, mainstream non gaming, if you want to save cash, i can play fine on my iball keyboard+mouse 16$ combo.
Speakers: Buy CREATIVE INSPIRE SBS A500 5.1 SPEAKERS SYSTEMS A 500: $62
The total should come to about 800$ give or take 50 bucks.
All the prices have been roughly converted from indian prices, so they might differ, most probably for the better.