Adult Website Enter Page

I need someone to design and code an enter page for my adult website that will still allow search engines to crawl all the pages of the website. My website is written in PHP but has a HTML enter page (for age verification and disclaimer). When the enter page is enabled the search engines cant crawl my site, thus I get pulled from the search engines. I need a popup window written in PHP or javascript that allows the user to click (enter) or (leave) after reading the disclaimer that they have to be 18 years old to enter the site. If they click leave I want it to take them to one of my other sites that is not adult. There could be a lot more work for someone if they do a good job on this enter page for me. I plan on making many upgrades and changes to my website as it is growing in popularity really fast. In the admin section of my website Im able to enable and disable the enter page. I want this feature to stay the same. Ultimately I would like the main page to load completly and check the user for a cookie, if no cookie present I want the website to load the enter page in a smaller window over the top of the main page with the main page bluring or clouding over to where you can just barely see the images. Once the user clicks (enter) the website send that user a cookie and the enter page shrinks and the main page clears up and they have full access to the website. If they click (leave) i want my other website to load in the background before the enter page shrinks and the main page clears up. I hope I have given enough detail about what Im looking for.