Use this below to send all SE hits to a landing page to filter them to a sponsor of your choice
RewriteEngine on
RewriteCond %{HTTP_REFERER} ^.*yahoo.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*google.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*msn.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*dogpile.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*altavista.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*lycos.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*webcrawler.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*overture.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*metacrawler.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*ask.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*infoseek.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*excite.*$ [OR]
RewriteCond %{HTTP_REFERER} ^.*bianca.*$
RewriteRule /*
http://putyourlandingorfpahere.com [R,L]