Custom page for guests

[Frosty]

Hey guys,
Is there a way to display a custom template to all guests, no matter what pages on the site they try to visit? I want to display a login form (nothing else) to all guests. If they aren't logged in, they won't be able to see anything except the login form.

I tried creating a plugin and the hook I used was global_start, rest was the simple stuff, just code for the display of a custom template wrapped in the usergroup conditional.. But it didn't work.

P.S. Forum and attachment permissions aren't the problem (I'd set them to 'no' for guests after I finish this), I just don't want to show the login form within the forum's style. I have the custom login form finished as well...

Thanks...