Xvfb is X Virtual Frame Buffer. That is, it doesn't use any real graphical hardware to display X. It just uses system memory. That way, you can have an X server running that doesn't require any hardware (if you had a serial console only, like under many big Unix boxes) and doesn't interfere with whatever hardware you might already be using for other purposes (like the standard text console for Linux and other PeeCee Unices which runs on what's usually your only graphics hardware).

The idea is that you can start up Xvfb and have your X-requiring processes use it as their DISPLAY. Anything they draw never gets drawn anywhere you can see, so you have to make sure that they don't need any interaction. If they do, you might need to look into using Xvnc, so that you could interact with it over VNC, if needed (in fact, I believe that Xvnc might use Xvfb under the covers). But you should be able to get a VMWare session set up so that it can start up on its own with no interaction needed, I think.