Create a Web User Control (ascx), then put your navigation menu code in the control. Once it's done drag and drop your control onto each of your aspx pages where you want a menu. When the aspx renders you'll see you menu.
Make your navigation control using an unordered list (<ul>) and listitems (<li>). Then style it up with css. (take a look at www.westciv.com and www.csszengarden.com for more info and inspiration)
<div class="navigation_holder">
<h2>Site Navigation:</h2>
<ul>
<li><a href="http://www.smartraveller.gov.au/" accesskey="1" title="PC users: ALT-1 -- Mac users: Ctrl-1">Travel
Advisories</a></li>
<li> <a href="/geo/" accesskey="2" title="PC users: ALT-2 -- Mac users: Ctrl-2">Country
information</a></li>
<li> <a href="/trade/" accesskey="3" title="PC users: ALT-3 -- Mac users: Ctrl-3">Trade Policy</a></li>
<li> <a href="/globalissues/" accesskey="4" title="PC users: ALT-4 -- Mac users: Ctrl-4">Global
Issues</a></li>
<li> <a href="http://www.passports.gov.au/" accesskey="5" title="PC users: ALT-5 -- Mac users: Ctrl-5">Passports</a></li>
<li> <a href="/minister/" accesskey="6" title="PC users: ALT-6 -- Mac users: Ctrl-6">Ministers</a></li>
<li> <a href="/geo/australia/" accesskey="7" title="PC users: ALT-7 -- Mac users: Ctrl-7">About Australia</a></li>
<li> <a href="/embassies.html" accesskey="a" title="PC users: ALT-a -- Mac users: Ctrl-a">Embassies
and Consulates</a></li>
<li> <a href="/treaties/index.html" accesskey="8" title="PC users: ALT-8 -- Mac users: Ctrl-8">Treaties</a></li>
<li> <a href="/publications/" accesskey="9" title="PC users: ALT-8 -- Mac users: Ctrl-8">Publications</a></li>
</ul>
</div>