You would need javascript / jQuery to do that.

Create an array with images and select a random one, then and set the bodies background-image to that image.

AFAIK, there is no ready made solution for this.

thank you!! I'm having some trouble with this part:

url(<%=skinpath/%>/images/<%=Int((3-1+1)*Rnd+1)%>.jpg)

do I need to change "skinpath" for the actual path, or should the word stay as written there?

have I removed the spaces properly?

right now I have the images in the skin's directory in a folder called images. is there a better way to do it/place to put them?

Thanks so much for your help!