Actually, i have not done this yet,..but to my way of thinking (and so much of this is a paradigmation of mentation...yours, mine and ours),...you may be able to use an elementary transparent jpg or gif file created with your graphics program (I use Jasc PSP). This should be able to 'tile' over any base image according to the rules to get it all to parse.
With your transparent image made,
Then use the Z-axis methods to make the layers as you want stuff to show. This may sound easier to do than in actuality. It involves 'stacking of positioned elements' which uses the z-index methods as the usual page positioning is only X and Y coordinates. ( i am still struggling with x and y positioning myself as an alternative to other options to place stuff and i hate tables). ... Think of the Z axis as running perpendicular to the pc screen so all the layers are like floating planes you can artsy as you like. As i said I haven't worked up one of these yet but i was just reading about it when i saw your post....there is more about it in Eric Meyer's book "Cascading Style Sheets, The Definitive Guide."
ISBN 156596226. I assume there must be info on z-layering at the W3 web-resources, but I find the W3 CSS resources difficult to search through, I imagine there is so much that is new that it is hard to keep it all well grouped there.
Of course a high-end web-graphics ap like Dream-weaver might make the task easy, i don't know.
Let us know if you can devise the effect 'cause plagerism may be the highest form of flattery.