Check if user logged in or not

[iadmirevb]

I have modified the navbar to include two new items. One that pops up a windows with a radio and one that pops up a window with TV.

I want to check that a user is logged in. If they are, then the pop up opens. If not, i want to redirect the user to the log in page.

So far, here's my code to open the pop up:
<!-- TV -->
<td class="vbmenu_control"><a href="#" onclick="window.open('http://www.mywebsite/tv.php','tv','statusbar=no,menubar=no,toolbar=no,s crollbars=no,resizable=no,widt h=300,height=375'); return false;">$vbphrase[tv]</a>
</td>
<!-- / TV -->

How do i add a condition to open if logged in and to redirect if not?

Thanks