One common culprit whenever you're having trouble styling something in DNN is that the standard default.css is always present and applied to all skins. This means that anything you have not specifically restyled in your skin.css might fall back to something specified in default.css. When you create new styles, always look in default.css and copy out and restyle any defaults you find in there... or just for fun, remove the default sheet temporarily to see what happens to your skin and fix it from there. Any individual skin should really be completely self-sufficient with its own styles and not rely on deault.css.
But more specifically: You're probably going to get better results if you apply link styles directly to images using this example:
a:link img, a:visited img, a:active img{border:1px solid red}
a:hover img {border:1px solid blue}
Insert your own colours there and put it in your skin.css
Also, have you added style sheet links directly in container or skin files... the site is generating two iis errors that I don't recall seeing the first time I looked. Try and revert whatever it was.
Also.. no excuses about this, just do it: Install the Firebug and Web Developer addons for Firefox. They are essential when troubleshooting css in DNN. Use the "right click Inspect Element" for Firebug and the "Edit CSS" menu item for the Web Developer addon.
Rob