It sounds like an issue with the URLs you're using. The question is, if you're using relative URLs in the CSS file, what are they relative to? Is it the location of the CSS file, or is it the location of the page that the link is on?
I believe it's the former, but my CSS has always worked in both places without error (I think!) and I've never really given it much thought. I use the following directory structure:
My background CSS looks like: { background: url(../images/image-1.gif); }
If your set-up is different to that then this might help you out.
Jules