http://www.facebook.com/terms_pages.php 7. Third party advertisements on Pages are prohibited. Ads or commercial content on Pages must comply with our Advertising Guidelines. can I post links to landing pages on my pages wall?
You must first see the advertising guidelines of the Facebook. Here you will find it facebook.com/ad_guidelines.php it's on # 2 on Landing pages/ Destination URL's.
This means that anything what is not related to the fan page should not be posted. For example you have a celebrity fan page and you promote something else will not be allowed. This is for the admins of the page. However if you wanna promote your site or product in some other fan page, you can do it but better take the permission of the admin of that page. Now-a-days you cannot even post anything on other fan pages, if the admin reports it to facebook, you will be immediately banned from the site.
If you want to advertise anywhere in the facebook you must comply on their terms and condition regarding advertisement.
Check out this http://www.facebook.com/ad_guidelines.php and http://www.facebook.com/ad_guidelines.php for your reference
yeah you pretty much can't advertise 3rd party or other business on your fan page that has nothing to do with your fan page. I know now it sucks that you can't even post on other fan page.
There are some rules that you must check before making a page or giving an ad into it.. Check the link above to get the info.