Gemini =
I would suggest that you ask your host to create a virtual directory for your content. That is what we do on all our domains. You setup one directory within your filespace as your content, the host can then redirect that directory to be a virtual directory such as /pics that each of your domains can hit, and no matter how deep you are into your site you do a simple call to /pics/catagory1/pic1.jpg. Then all you have to do is add a line each time you add a domain to your site pool
It's pretty cool actually cause you can save on disk space if you tend to use pictures over and over and have multiple copies sitting around. If you need a step by step, just let me know and I will do so when I get back from the weekend, got a wedding I'm heading out the door right now. Take care all, have a good weekend.
Tim