I have a site that has been up a few months and is listed in the serps. I've decided to break it up into 3 different sites ( each more narrowly focused ) with 3 different domain names.

Do I leave the site up at the current domain name and take the sections to the new domains or would this hurt me in my search engine listings? Is this considered duplicate content?

Do I just put a doorway page there leading to the other sites?

Need some help, please.

Is there any programming language which best suits SEO? Does dynamic programming language such as asp.net creates any problem for SEO?