Help to make a random code apear

Hey everybody!

I'm going to make a cool project working on my forumotion site, but I can't make the last part work.
Can somebody please tell me how I can view a random code on a page, so it's not the same everytime a user/guest se it? I got these two codes i would like to switch between.

1. Code:

Code:

<center><br/><a onclick="window.open(this.href,'DigiviceJagt','resizable=no,location=no,menubar=no,scrollbars=no,status=no,toolbar=no,fullscreen=no,dependent=no,width=300,height=200,left=500,top=250,status'); return false" href="http://digimon-world.danskforum.net/Digivice-Jagt-FS-h51.htm"><input class="liteoption" type="button" name="" onclick="document.searchform.google.value='';" value="Digivice Jagt" /></a><br/></center>

2. Code:

Code:

<center><br/><a onclick="window.open(this.href,'DigiviceJagt','resizable=no,location=no,menubar=no,scrollbars=no,status=no,toolbar=no,fullscreen=no,dependent=no,width=300,height=200,left=500,top=250,status'); return false" href="http://digimon-world.danskforum.net/Digivice-RS-h54.htm"><input class="liteoption" type="button" name="" onclick="document.searchform.google.value='';" value="Digivice Jagt" /></a><br/></center>