I wanted to remove the underlined links from Safari and found that if you go to /Applications -> Safari.app -> Contents -> Frameworks -> WebCore.framework -> Versions -> A -> Resources -> html4.css, then you can edit the stylesheet near the bottom where the CSS Selectors are located. For instance, here's what mine looks like:
<--Of course, you can edit it how you want to, or use your own.
a:link { color: blue; text-decoration: none; }
a:link:active { color: black; outline: gray 1px dotted; }
a:visited { color: navy; text-decoration: none; }
a:visited:active { color: black; outline: gray 1px dotted; }
a:hover { color: red; text-decoration: underline; }
-->
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030110064312507