Alienware are expensive, it's a bit like buying clothes - the Tesco Value jeans may look and feel the same, but you can't say their Fubu can you???
Take a look at http://www.mesh.com
, their a UK company but they might deliver to the USA. The 4800+ is way higher than what you need, and unless you wanna pay around $650+ for the CPU alone then don't get it. The X2 3800+ or the X2 4000+, even the X2 4200+ are the ones your looking for.
If you want future proof, go dual core. If you want to save money, which you obviously don't need to, go single core. So dual core is your way forward