Okay, I have it working somewhat. What I did was download the script from that page and uploaded it to my server. I then added the following code to my header-insert:
<script type="text/javascript" <br />src="http://www.drumlines.org/scripts/styleswitcher.js"></script> <br /> <br /><link rel="alternate stylesheet" <br />type="text/css" href="http://www.drumlines.org/betathreads/stylesheets/aqua.css" <br />title="aqua" /> <br /> <br /><link rel="alternate stylesheet" <br />type="text/css" href="http://www.drumlines.org/betathreads/stylesheets/mocha.css" <br />title="mocha" />
I then went into ubbt_header.tmpl and changed:
<link rel="stylesheet" href="$stylesheet" type="text/css" />
to this:
<link rel="stylesheet" href="$stylesheet" type="text/css" title="default" />
I then made a post, in HTML, of this:
<a href="#" onclick="setActiveStyleSheet('aqua'); return false;">Change style to Aqua</a> <br /> <br /><a href="#" onclick="setActiveStyleSheet('mocha'); return false;">Change style to Mocha</a> <br /> <br /><a href="#" onclick="setActiveStyleSheet('default'); return false;">Change style back to your default.</a>
It affects all users, not just you.

If anyone knows a thing or two about cookies, I'm sure that will solve the problem.