alt131 - 10:20 am on Mar 11, 2012 (gmt 0)
ooooo ... "t" word alert ... this is what happens when you stop the haddock-slapping and start with magenta/cyan colour schemes ;)
Myrrh, you always ask interesting questions, and you and Lucy have been progressing through this one, but I wonder if it would help to pause and consider where you've come from.
To answer your question, yes it is possible to set multiple background-images on the same element. See
3.3. Image Sources: the ‘background-image’ property [w3.org] for more detail. However, this is only supported by the most modern versions see quirksmode [quirksmode.org] so not so helpful at this stage.
However, as I understand it, what you really want is a different background for the page, header and footer which is not the same as setting multiple backgrounds on the same element. For different images, the most practical solution will be the one that delivers the desired result with the least complicated code, smallest file-sizes and least server hits. Again css3 provides non-image based options for gradients, but support is sketchy and I've found them to be so slow that a 1px repeating image is likely to be faster.
I think useful to separate the issue of background-images from the issue of the footer layout. Again, as I understand the thread, you've figured how to set the background-images for each element which resolves that. That takes us to layout, and Lucy's suggested document structure is roughly correct, then I expect the footer is "hanging" about 20px below the header because the elements in between are floated or positioned. Given the references to the footer being above/below the content, I'm with Lucy that positioning is a likely suspect.
Finally, are you sure you want a sticky footer? That's a footer that sticks to the bottom of the viewport if there is very little content, but slides down to the bottom of the page if the content extends below the fold. Unless you really want the sticky part you just need an ordinary footer, which needs a different approach. I realise you've already done a lot of reading, and I imagine you've come across lots of conflicting explanations as well, but Paul_o_b has some really readable posts on sticky footer issues, plus working code samples. I think these three are the most relevant here - ignore the thread titles, just look for Paul's posts, especially the last which contains a basic page structure that should get you going.