For $5700 I not only bought those specs I mentioned but I also added two thinkpad T60's. Now that's a deal. Dual Core 2.16ghz with 1gb ram (can take 2) 120gig HDD and a 128mb dedicated mobility radeon graphics card, dvd/cd burner and so on... 

If you've got 4-5k to spend, get an upgradable desktop (you dont need 8gb ram that's THAT expensive, ((max out at 3 to start)) there are cheaper boards and you dont need SLI or even an aftermarket fan & hs if you're not going to OC) then add a nice laptop to the mix. You'll not only walk away with a desktop that will last you the nxt 5-7 years and be vista capable (when vista is capable that is) but you'll also be mobile.