My FaceBook Page is setup so that users who have not \"Liked\" the page yet (and attempt to view the page) are presented with the content of a particular tab instead of the
Apparently like buttons aren't supported in the current implementation of FBML, which is the only language you can use inside the "tabs" on a facebook canvas page. You may notice that a number of professionally done sites put a big arrow pointing up and then a "click the like button" text, without actually using a like button. This is why they do that.
Until facebook implements XFBML inside tabs, it looks like any XFBML only tags (such as fb:like) can only be used on your personal website. I think they do this for security reasons, although it does seem a little ridiculous that there are features you can use on your own page that facebook doesn't actually support on -their- pages.
The only workaround I have found is to include fb:comments tag in your app, which is an FBML tag that puts up a comments box AND a like button.