I have a feeling that it will work,BUT you wont be able to over clock in the bios like the qx6850 or extremes.I do think this could be fix with a bios update
Few enough motherboards support the 1600MHz FSB of the QX9770. Plus it's not really worth the money anyway.
EDIT - There was a thread where someone got the QX9650 working in the XPS 720
Asus Rampage, Q9450 @ 3.2GHz, 4GB DDR2 800MHz (4-4-4-12), 8800GTS 512MB
X-Fi XtremeGamer, 4 1TB HDs, Triple Boot - Ubuntu (Hardy), XP Pro and Vista Ultimate 64bit