How to do random header image?

[tdem]

Hi everyone. I'm trying to improve my sailing clubs website, and was working on a theme for getsimple.
http://www.tdem.co.nz/nbc/

I tried to implement a random header image using this script here:
http://www.alistapart.com/articles/randomizer/

Now, I've tried setting the background image in the css stylesheet by referencing this script, and by hardcoding an image in the template, with the script as source.

In both cases the random image only works if you refresh the page, and even then only sometimes. On my test wordpress install (default theme)
it does work flawlessly on all browsers, but I can't figure out what is used here to accomplish this.

Does anyone know an alternative way of doing this? (Not javascript please)

Any feedback on the theme itself (which isn't finished yet) also welcome.

Thanks, Thomas