How do I detect if user is logged in?

[kwame]

Thanks for the help but I guess I should have been more specific. The code is going to be placed in the header template and once I put the code
<if condition="$show['guest']">Login</if> into the template, I immediately get errors. Any thoughts?
Kwame

The error that I get is "Parse error: parse error in E:\jamproinvest\caribbeanbusinessclub\forums\globa l.php(512) : eval()'d code on line 368" and line 368 is the line that says "<if condition="$show['guest']">"
Kwame