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Wow there Half-dead.
Sounds like your talking about cloaking. From
Search Engine World:
Quote => Using some system to hide code or content from a user, and deliver custom content to a search engine spider. The word Cloak comes from Star Trek where the Klingons were capable of "cloaking" their ships invisible. There are three main types of cloaking: IP based, User Agent based, and the combination of those two. IP based cloaking custom delivers a page based on the users IP address (this can be used to deliver custom language based sites or target groups of users from particular ISP's such as AOL or @home users). User Agent cloaking sends a custom page based upon the users Agent (most often use to take advantage of a particular agents strengths or features). Finally, the combination of Agent and IP cloaking is use to target specific users <= end quote
There are two schools of thought when it comes to cloaking. The search engines say "don't do it. It's spamming and we don't like it." and the web masters say "The search sites use cloacking themselves (ever tried to get to altavista US and ended up in UK or where ever your from) so it must be OK. And also if you don't catch us, what you don't see don't hurt."
Your probably thinking, if the sites cloacked how could the SE's see you. Well the occasional human does actualy confirm a proportion of listings. They compare your real web page to the one in the spiders cache and if they don't match
However if the only dif is the meta tags then a human will never notice, right, wrong. One of the first checks is a simple bit count. If the cached page has a different bit count form the real page then further investigation is taken.
Basicly what I'm saying is cloaking sections of your site can be very veryuseful but also fraught with danger. For more info check out these two articles
Here and
here.