How do Live DVD/CD/USBs detect video card and configure X accordingly?

I'm trying to create a USB that I can carry anywhere with my system on it, I know there are Live distros that can be used that way, but I need a very specific installation. The problem is that the USB will be used in a wide variety of machines with different hardware and sometimes the video only has a couple of resolutions available while booting with a live CD in that same machine provides more resolutions.

How do distros detect video card, load modules and configure X so that they can run in almost any computer (video wise)?

Edit:

I've seen in the Debian doc that if xorg.conf is missing (which is my case) Xorg will probe your hardware on every startup. So I did an apt-get install firmware-linux-nonfree (I have Debian stable) and installed the xserver-xorg-video-????? (most popular video cards) and for now a couple of tests have been successfull. When more systems are tested I will post the results.