Dell XPS – Using Two External Monitors with Dell XPS 15z

The Studio XPS has a Radeon HD5730, which should support Eyefinity. Using the VGA port and DisplayPort simultaneously should be possible; however, you will not be able to use the built-in display at the same time. You can either have the internal display and one external display, or two external displays, but not all three. If that still isn't working, try updating your graphics drivers to the latest version from ATI (not from Dell's site) and see if it works then.

Yes you can, at least according to this forum thread (about two thirds down)

Relevant bit quoted:

YES, it is possible to connect two external screens to XPS 15. However, you need to disable the embedded laptop screen for the time being. You may NOT be able to configure it using your Win7 "Personalize" context-menu option nor by using keyboard but it can be easily done via NVIDIA Control Panel (use the checkboxes).