for the whole document:
<style>
a:link {text-decoration: none;}
a:visited {text-decoration: none;}
</style>
if you want to do it for a group of links, you should create link "classes"
<stlye>
a.ClassName:link {text-decoration: none;}
a.ClassName:visited {text-decoration: none;}
</style>
<a href="page.html" class="ClassName">click</a>
hope that helps.
~Quack