Creating virtual hosting by programing

Hi,
Want to create virtual host from my web site using pages e.g jsp, asp.
As tripod.com, weblogs.com and freeservers.com are doing. i.e when user registers its name, they creates site for them like hamid.weblogs.com on the fly. Taking name from input file and create the virtual site agains the name.
I also wants to do the same. When user enter its site name, the routine takes the name and creates the virtual host for its name.

Hoping for quikest response.

Hamid Hassan