D600 with three monitors.

Quick question. I'm on a D600 an have the docking station. I've been using the VGA with an external LCD for a while now to extend the desktop to both screens. I just got ahold of a second LCD and though I'd try and hook it up on the DVI connection. The question is can I get all three going at once? I can drive both the externals at once, and any combo of two, but can't get to three. The Mobility Radeon 9000 says it supports three monitors and XP claims to handle up to ten. Is this possible? I can't get the third monitor to show in the Settings panel of the Display Properties but it's there in the Advanced. (Won't enable it as it says that the desktop would not be visable.)

Ideas?