computer

[Charge]

~ $2000-2500 and you have WHOLE computer which is enough for most games at max..

[Lemur]

Hmm, a little more realistically:

You can build a rocking game PC for around $1k. That's without a monitor. You can have a no-name company assemble a great game PC for between $1.5k and $2k, or you can buy a boutique gaming PC from Voodoo, Alienware or Falcon Northwest for $7k.

But the only way you're gonna play high-end games for $400 it to buy and Xbox 360. And bear in mind that the online component of that ain't free.