I have to agree with Bill, just seems pointless, yet another clever, but pointless geeky solution. Another point to consider is that the whole Javascript thing is completely useless if the user also has Javascript disabled. Always go for a CSS solution over Javascript. I can never understand why people use javascript to swap background images for navigation anchors, when you can do the same with CSS.
with the JQ image replacement, I have to also point out that this method is not exactly in keeping with the ethos of keeping content and layout seperate. A fancy heading graphic is not vital either. Having a graphic between a heading tag is totally inappropriate and blatant miss use of the heading tags.
I prefer to use the span method as demonstrated in the last of Bills links, assign an image to a span, set to 100%, covers the text up. This is also useful for links , just set the span inside anchors, and hey presto you have a fancy graphic, that is being kept separate from content and layout etc, which is also completely clickable.
Anyway, you decide what you go for, but please do not touch javascript for this solution.