You can't revert back to a previous version of OS X once you installed Lion. You're going to have to wipe your drive.
Best thing you can do as far as getting data off of it, take the hard drive out and put it in a USB enclosure, use another Mac to connect to it and pull data off. Alternatively, use another Mac to make a thumb drive with OS X on it that you can boot to, boot to that then try to salvage whatever you can. You can try going to an Apple store but it'll be hit or miss depending on the manager and how nice they feel at the time.
Everyone else is chastising you for using pirated software. Obviously, you shouldn't be using it at all, but hey I understand that people like to try new things especially when they aren't necessarily allowed to. Let this be a lesson, next time install onto a new partition, never use pre-release software as your main software, especially when it comes to OSs.
EDIT: Nevermind, guess you fixed it. That's what I get for only reading the first page of a topic before jumping to reply!