Is it possible to allow only search engines to view the content of a site?

I want search engines to view the content of my site, but I do not want regular users to view it unless signed in. I have seen this done on forums where you have to pay for it. Is this easy to do?

Its called cloaking and frowned upon.

What is wrong with doing it? I want people to know I have content related to there topic, but I do not want people viewing the pages without signing up.

Ive seen somthing like that before, but yea, google doesnt like it at all when you dont show the users the same thing its seeing. In fact I think (could be wrong, im no expert) it can get you thrown out of googles index.

But in answer to your question, yes, it is very possible to show google one thing and visitors another.

That's correct. Cloaking can cause your site to be sandboxed.

So what webmasterworld.com does isn't allowed by google?

Ty lol, that was the site I was looking for that confused me too.

Looking at some stuff, it looks like links to there site may have a lot to do with it.

googled site:webmasterworld.com and came up w/ 221k+ results

Most of the links point directly to specific pages, which is what you want anyway.

That is allowed by Google I suppose, because your not necessarily showing google one thing and the users another, nether can see the page being linked too but Google can see that the link exists.

Would that be possible?

I can tell you that they have done it for a long time. I am sure they know what they are doing as well, cause they seem to be on the ball on the site. They are showing the content or something to them somehow, not sure exactly how they are doing it. I would like to do something like that if it won't get me banned from google.

I would really like to know how they do it too, it has got to help with signup's im sure. Ill look/ask around and report back if i find anything. off to vBulletin.org i go

Here is an option. Not exactly what you are wanting, but could be effective.
Limited Guest Viewing -- Improve community registration rates - vBulletin.org Forum

but wouldn't that hurt google anyway? Aren't they going to get the same error message?

Actually, probably not. Sure a lot of content would be missing but think of the way a Q n' A forum works, someone asks a question, then others answer it.

More people are bound to type the question in asked in the first post than they are the answer (hidden by vBulletin).
Not a half bad idea IMO.

Good find Mike!