If, in Dreamweaver, all of the links, for example, are written <img src="....">, and the links are written <a href="..."> then you can use the find/replace with the 'entire site' option, rather than just the 'this page' option.
e.g.
FIND: <img src="
REPLACE WITH: <img src="/assets/images/
and similarly for all the links.
There is also a 'find/replace in selected sites' option, so say, for example, you had multiple 'gallery' pages, where the images for each page are in different galleries, you could just change the path to the images for selected pages. (Does that make sense?).
Sorry, I haven't got Dreamweaver running here at work, so I'm not sure on the exact phrasing/location of these options, but I know it does it - I had to do it once!
