I think he wants to create this effect himself.
Dummy code:
<a href="link" on mouseover="display a new picture, PNG format, 8-bit transparency"><img src="normal link picture" /></a>
You need JavaScript and PNG-okay browser, as well as miniaml Photoshop skills to create correct transparent PNGs. That's not a so bad idea in the end, I'd like to do it but I'm not sure if it'll render nice. What worries me is that your normal picture and your hover picture will be of different size, and that's not recommended.
Otherwise it's true Flash would make a good job of it all. uoba rules, look at his site.