sites With Examples for Creating user and adding user to Sharepoint

Code Snippet
//1) Create membership user

MembershipUser membershipUser = Membership.CreateUser(login, password, email);

//now you have it



//2) Create sharepoint user

SPWeb spWeb = SPControl.GetContextWeb(HttpContext.Current);

//get your site instance

SPUser spUser = spWeb.EnsureUser(login);

//now you have sharepoint user



//3) Add sharepoint user to a desired group

SPGroup spGroup = spWeb.SiteGroups["VISITORS"];

//get your group

spGroup.AddUser(spUser);

//that should do the work


http://social.msdn.microsoft.com/Forums/en-US/sharepointdevelopment/thread/db46ab8f-9594-4878-9bab-a18fe3fba959/