I made a big website using that program and want to use other hosting services. No I am concerned that it might have a certain feature that only allows you to use their hosting serivice. I hope not, I like 1&1 Internet much better.

There should not be a problem unless your site has ads from the Sitebuilder. This would make odd having a site on 1&1 designed in Yahoo SItebuilder. Contact 1&1.