Depends. If you want software and stuff for it, and don't want to deal with any hassle of components or doing extensive research, I'd say just go with a Dell.

If you're going to build one, as a general path, I'd go with one of the new chipsets that Intel just released yesterday, and a E6700 processor which you can pick up for $320~. You can definately build yourself a way sweeter machine for the same price you'd pay for a Dell. Any of the Dells that are reasonably priced, around 1000, are at least a year behind with their specs, so I'm just not a fan of shelling out a grand for old components.

Like the cheapest Dell you can get that uses that $320 processor I mentioned, is like $2000, which is nuts.

Processor + Motherboard = $500
Graphics Card = $350
2 GIG RAM = $200
HD = $100
Case = $50

Scavenge a CD-Rom/Mouse/Keyboard from your old PC, and you'll save yourself like $800 bucks over a Dell. Once again, you're getting no software though.

If all you want it for is SC2, the $1000 Dell will certainly run on any of those though I would think, since RTS games are generally not cutting edge graphics technology.