Automated webspace for member

Hello, we have a group and want to offers our members free webspace to set up their own webpages (frontpage sites, asp. sites) etc. The server we use is windows 2003 server with PLESK 7.5. What we want: we are looking for a system which can automate the creating of webspace for users (automation means: creating subdirectorie with the choosen name of users, install frontpage extensions if needed). There must be a possibility to pay if they want more than the normal webspace. As control system, we can create a frontdoor which opens only when a member logs in. It is clear that each member may only have one webspace. thanks