You'll get a much better system if you build it yourself.
Most places will mark it up a few hundred bucks, if you have them build it.
Building a system is pretty basic, especially with all the tutorials and guides for it.



I'd go with an i7 920 processor, the stock cooler is fine unless you're overclocking in which case grab an after market cooler.

Go with a decent motherboard, I like Asus but there are a lot of choices out there.

Probably 12GB of DDR3, although 6GB is enough for boxing alone.

The Radeon 5870 is a really nice card, or a GTX 285 if you prefer Nvidia.
Generally speaking, SLI/Crossfire is not much of a gain for Warcraft, but can be for other games.
Also, the X2 cards with two cards on one chip are generally a subpar option for Warcraft as well.
Depends on how much you're playing WoW vs other games.

A SSD drive purely for the gaming folder, is a huge boost.
I went with a 64GB Patriot Torqx; I like Patriot, but again there are other options.

Probably a pair of 24" monitors would be fine in the budget you have alloted.
One for the active toon and one for the slaves/alts.