how do I put a close button in a popup window

[Suddaan]

I have got a few pop up windows on my web page but I want to add to the popup window the abilty to click either a button or a link [click to close] to be able to close the window.

Thanks

[Spookster]

<form>
<input type="button" value="Close" onClick="self.close()">
</form>

or

<a href="javascript:self.close();">Close</a>