I think your path isn't correct.
Try something like this instead:

body { background: url(mysite/images/background-{$RandomBackgroundNumber}.jpg) 20% 20% no-repeat; } 

Just put the path to the images in there, relative to your website root.

As a test I did the full images directory root with this:

(this is what the URL looks like until I activate DNS)

		
<style type="text/css">
			body { background: url(http://sonic.net/~carrera/carrera-marble.com/themes/carreramarble/images/background-{$RandomBackgroundNumber}.jpg) 20% 20% no-repeat; }
</style> 

still does not display a background.. thoughts? or did I do that completely wrong?

Uhh. looks fine to me.
Although relative paths like I described should work just as well.

Please have a look at the (generated) source code of the Page and tell us how your css style looks there...

yeah it looks fine because it was HAHA.
I looked at the source code and it was calling to background-5.jpg
and I only have background-1 through 3.

How can I tell it I only have 3 backgrounds?

	function RandomBackgroundNumber() {
	return rand(1, 3);
	}

I did that because the original had a 6 there. But it still wants to look higher than 3.

Thank you SO much for the help here!