I need help adding an additional monitor

I want to add run two monitors with my Dell XPS Gen 5. Do I need a new graphics card or a DVI switch of some kind??

Straight from the ATI website describing your ATI Radeon X850 XT graphics card…
Display Features

    * Dual integrated display controllers
    * Dual integrated 10 bit per channel 400 MHz DACs
    * Integrated 165 MHz TMDS transmitter (DVI 1.0 compliant / HDMI interoperable and HDCP ready**)
    * Integrated TV Output support up to 1024x768 resolution
    * YPrPb component output for HDTV display connection*
    * [B]Single and dual link external TMDS transmitter support for high resolution and/or multi-monitor DVI configurations[/B]
    * Compatible with ATI’s THEATER™ video decode and capture devices for VIVO (Video Input / Video Output) configurations

Plug your second monitor into the additional DVI port…
Go into Display property>settings>Activate second display…
So the quick, fast, and in a hurry answer is YES…