Thank Ivan, you're super!
Just a last question, in my current implementation of User's table I have got no GUID (I use an int identity), I've seen that setting the property it called
public override Telerik.Sitefinity.Security.Model.User GetUser(System.Guid id)
throw new System.NotImplementedException();
what should I do here??
Need I to supply a table with a mapping between my ID and the GUID?