With that budget you definitely cannot afford a "beast" computer, but for that price range I would recommend an Intel Core 2 Duo processor (E8400 is best value for money). Get DDR2 800MHz RAM, also best value. Make sure that the motherboard you are going to pick supports DDR2 and Dual Core. I recommend an ASUS board, with a P43 or P45 chipset. Take the cheapest one, that is if your not planning on overclocking. Power supply: Corsair 550/620W. Case: anything thats cheap, but you might be looking for a CoolerMaster HAF932 ... great value for money and best cooling for it's price range. Or look at the slightly cheaper option, Antec 1200. HDD: Western Digital. Graphics card: for gaming, GTX 260 or HD 4870. For general use just get a cheap NVIDIA card on sale. Integrated sound/networking ... stock cooler ... buy and CD/DVD drive, preferably Samsung and also for a monitor, Samsung.
Thats just my idea. any questions feel free to ask.