Crossfire or SLI, a 1TB drive, a quad core, and all this needs to be overclockable... for under $1000? lol goodluck. It can be done but some parts will be less than quality. You can have a 1TB drive, quadcore, 8800GT, and overclockable components for under $1000, but SLI or Crossfire is going to push this thing over budget.
Here's a solid crossfire build with your 1TB drive:
$225 - ASUS P5E X38
$200 - Q6600 from Microcenter (hurry before they sell out)
$340 - Two Sapphire HD3870 512MB
$230 - 1TB HDD
$100 - 2x2GB G.Skill PC2 8000
$97 - Corsair TX650
$50 - Tuniq Tower 120
$30 - 20x DVD Burner w/ Lightscribe
$85 - CM RC-690
This assumes you already have a 64-bit operating system, monitor, speakers, keyboard/mouse, etc.
Why a single 1TB drive? Two 500GB drives in RAID0 is not only faster, it's cheaper! And I really don't think you can cut many corners off that build without losing significant performance, but some suggestions to lower the cost:
-Get 2x1GB of DDR2 800 for $30 instead of 2x2GB for $100.
-Get two 500GB HDD's
-Get a cheaper X38
-Crossfire HD3850's instead of HD3870's
-Get a cheaper case
-Get an IDE DVD burner, or just a DVD ROM
-Get a POS PSU
-Go with stock CPU cooling
Like I said, I don't recommend any of those alterations (with the exception of the 2x500GB drives), but they could be done and still fit your criteria. I suggest you increase the budget or give up on the Crossfire/SLI aspirations.