[Newbie] virtual hardware screen in desktop window

Hello,

I hope that this is directed at the right mailing list. If not, please excuse, 
and if possible, show me the way to the proper list.  I hope I'm in the 
ballpark, at least.

I am very unfamiliar with X programming in general, being a low-level systems 
programmer.

I would like to be able to somehow define a virtual X screen with a 
non-regular WxH size that mimics some custom hardware display device and 
lives inside a window on my regular X desktop (Fedora Core 4, stock).  I 
would like to be able to write X applications that use that screen, and then 
be able to switch with minimum pain to the real hardware.

I would of course be writing the low-level OS drivers for the custom hardware.  
I would also probably need to write some sort of X driver as well??

I am assuming that this has been done before but cannot find word one about it 
using search engines on the Internet.

I thought to use Xvfb but am getting a fatal error when I try to define a 
screen of 500x300x1.  Basically I want to simulate an LCD display, perhaps 
zoomable.

Can anybody here at least throw a few buzzwords my way that I can use to 
effectively search for how to do something like this?  Perhaps direct me to 
some sort of documentation site that talks about X server programming?

Thanks in advance for any help.