How to make "headless" system?

[Dennis Wicks <wix@mgssub.com>]

Greetings;

I have a number of older PCs that I use for testing/local 
webservers, fileservers, backup machines and other stuff. A 
couple of these have "glass ttys", ie. no graphics at all, 
and others have old low-res monitors of 800x600 at best. 
Also, they are all in the basement, which is a trip I don't 
like to make very often!

I want to force these systems to support hi-res 1680x1050 or 
better so I can VNC to them from my main machine and be able 
to use graphic software to operate and maintain these machines.

Right now I mostly use ssh and it can be a real pain!

Can anybody tell me how to accomplish this or point me to a 
"How To" somewhere?

I am running Jessie and XFCE.

Many TIA!!
Dennis