First: I really don't know anything about Linux, so I have no clue how well this will work for Linux, but heres a $2000 gaming PC
I'm assuming you already got Vista or are just waiting for Windows 7 (use RC 1 now) (plus i know you're going to use Linux some of the time)
I'm going to use newegg for the parts because they are amazing.
In the end I really tried to push upwards towards $2000 (I even through in a second graphics card, and gave you a CPU cooler, because you said you might want to OC) but in the end it came to around $1700
Here's a build w/monitor that also includes two gtx 285's running in SLI. gtx 285's in SLI > 4890's Crossfired. btw you can turn down or even turn off the bue LED's with the adjustable control knob on the outside of the case if they are too bright / too flashy for you. This build is also set up to over clock like a champ!
Make sure you flash to the latest bios with this mobo and then dl the latest drivers for it.