The reason stretching the nav is a problem is because when you hover over a link, the rest of the links move. It's sort of weird. You could consider changing of the colour of the image instead of stretching it.

For the pictures, you could consider creating thumbnails of each image, then only loading the image when they click on it; in that case, you're prevented from loading extra media the user doesn't want, saving you both bandwidth. In your case, it's really simple: just save each image as a 75x50 and append _thumb to the filename, then you can do this:
[code]<a onclick="renderImage('images/footage/0004.jpg')" href="#">
<img width="75" height="50" src="images/footage/0004_thumb.jpg">
</a>[/code]


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