[GameWizard]

Any standard popup code will work, simply search google for "Javascript Popup" or something along those lines. And if you want it to appear only for unresgistered, you will need use a conditional as follows:

<if condition="$show['guest']">
popup code
</if>

And if you want it to open up automatically you will need to add the javascript function to the body "onload". You can google this as well to know how to do it.