I have a Dell Latitude E6400, for which I purchased the following docking station:
http://www.amazon.com/gp/product/B002L9D320/
The back has two DVI inputs and one VGA input. I already have two monitors hooked up to it using DVI, but it appears I can only use one of my monitors in place of the laptop's viewport rather than in conjunction with it.
Quick and dirty research points to the use of a USB display adapter, but I don't want to use that since I hear those use the computer's CPU to render the display and I can't sacrifice any more CPU than I already am.
Edit: I should have clarified better that what I want to do is use my laptop screen in addition to the two monitors plugged into it. Thus, there will be three total viewports.
Best Answer
Nope, this will not work with three monitors. I have an E6400 with the Dell docking station and it will not let me use more than two (including the built-in display). It's limited by the on board graphics controller per Dell Enterprise support. I have had this question asked a few times by users in my office with E6400's who would just like to use two monitors and the built-in display.