How to do a hidden html visable with a javascript function?

How to do a hidden html visable with a javascript function?

I'm trying to do a hidden HTML visable, by running a Javascript function.
This is the hidden div I want to get visable with a javascript function:
<div id="Signup" class="modal hide fade LoginSignup" tabindex="-1"
role="dialog" aria-labelledby="myModalLabel2" aria-hidden="true">
Some content*
</div>
Right now I'm using this button to show the hidden div content:
<li>
<a href="#Signup" role="button" data-toggle="modal" class="btn
btn-success">Sign Up</a>
</li>
Is this the best way to do it? Or is it an other way to get a designable
pop up window?