On a Facebook Fanpage, how do you Iframe a site?

I was on a fanpage earlier, and it said:

step one: become a fan
step two: invite your friends to become fans
step three: click here to make sure you've completed step two

But then it went to another site, but only inside the frame, the facebook header and tabs were still there, but now there was a gateway website blocking the content in the center of the facebook page.

It made me jizz in my pants just a little.

How do you do that?

Is it part of your fanpage, or if you put a link on a fan page, is that how all links will open?

Just wondering how to do this, or if this is allowed, as putting a link to a gateway website as part of a fanpage seems like it would be banable?

look for the FBML page, you can join it and add it to your page, honestly people are going insane with this