Disable unregistered users from viewing post / But allow SE to index
 

I am trying to figure out if is possible to set the permissions of the forums and threads so visitors must register to view them, but I want the search engines to still be able to index them.

It is not a concern of non members seeing content that is only available to members, but a matter of increasing signups. Is there a way to let vbulletin know it is a SE and allow them to index all content? I hope I am explaining this clearly enough. Any help would be greatly appreciated.

A SearchBot is just a visitor in teh Unregistered/Not Logged in Usergroup and will follow the same permissions. It is not possible to make a difference.

It would even be against the TOS of all SE's to present different content to them as to Guests, and they would remove your site from their pages if they notice (and that is not unlikely)

What you could do is create a Usergroup "Search Engines" and give this Usergroup all necessary Permissions.
Then create a Plugin (or File Hack for < 3.5) to make SE member of this Usergroup upon access.

But I think it's not a good idea to force Users to register - you will just end up with tons of inactive accounts.
Users that are interested will register anyway, and those who are not interested are worthless.

Furthermore, this could be considered cloaking and might get punished by Search Engines.

Just my 0,02 €

Wouldn't that create a huge security hole though. because I can easily forge my "Browser Agent" and fake it like I'm a searchbot and have full access to the forums.

Well you all have good points and I didn't look at it like that. Thanks for your opinions, I will just leave the forums open for viewing and work on creating interest so visitors join.