Quick question on a conditional

I've got a page (webtemplates) that I use to load a separate page in an iframe for content. What'd the correct conditional be for the following (pardon layman's terms):

If - Registered User
Show - <iframe>loggedin.html</iframe>

If - Guest
Show - <iframe>youneedtologin.html</iframe>

Would something like:

<if condition="($show['guest'])">
<iframe>guest content</iframe>
<else />
<iframe> logged in content</iframe>
</if>

Would that be correct?

Thanks as always.