basically we can't have a script that can be used in all the scenarios that our customers have, but we can guide you through the process. First thing that you need to do is let us know how your user related data model looks like. After that we can guide you through the process.
Basically you need to import your user data into three database tables, first you need to insert data to a Aspnet_Users table, then Aspnet_Membership table (take a look at the ASP.NET Membership model and providers on the MSDN) then you need to import roles in the Aspnet_Roles table and connect the roles to users in the Aspnet_UserInRoles table. Then you can copy other user data to UserProfile table.
Let us know if you need anything else.