Yes! You've got two options - when you sign up you can import your site. BigTurns does it's best to import all your pages and so forth into the system (use the advanced sign up though). Alternatively you can create a blank site and FTP all of your pages up to the system. There are some limitations to this though - it won't create any Templates - just web pages, and it can only bring across the pages of your site. Some Blogs can also be imported directly,

Special parts of your site will need to be recreated like your shopping cart.