XSL Programming

Hello,

Probably an easy one to answer.

In this chunk of XSL:

<a>
<xsl:attribute name="href">
<xsl:value-of select="SiteURL" />
</xsl:attribute>
</a>

This returns a URL like so:
http://www.site.com

If I want to add something to the BEGINNING of http://www.site.com and have
NO ACCESS to the database where this link sits, how can I manipulate the XSL
to do this?  For example, I want instead:
http://www.mywebsite.com/tracking.asp?Link=http://www.site.com

OR

http://www.mywebsite.com/tracking.asp?Link=<xsl:value-of select="SiteURL" />

Not sure how to go about this, anyone have any ideas?

Gary.