I only recommend building your own computer IF you know how to built one. I have been building and repairing my own systems (and for others) for more than 15 years now.
If you don't know how to build your own system, then buy something like boeing247 suggested. I don't know the prices of those systems because I never look into them. I know all about the CPU's, GPU's, RAM, MB's etc., so I build the best system I can, with the money I have available to spend on it. Also. Because I build my own systems, I can upgrade CPU, MB and RAM, while the rest of the components can be brought into the system. This greatly reduces the cost of a new computer.

I generally do this every two years, but events beyond my control (my daughters wedding, my eldest sons 21st birthday party and youngest sons 18th birthday party) may push me back a year. My wife was also supposed go to the Philippines this year to visit her family, but she couldn't go, so she will go next year. So it looks like I might have this system for 3 years instead of 2. That's life!

My suggestions are as follows:

CPU	-	i5 2500, i7 2600 or i7 2600K
RAM	-	8GB
Graphics Card	-	High end Nvidia or ATI
Operating System	-	Windows 7 64bit

Mark