I have a similar question that might actually help you.  Here is how I used to add a user to a "Security Role" back in DNN3.  I migrated to DNN4, however, and now this piece of code SOMETIMES assigns the user to the role and SOMETIMES it doesn't.  I have heard this is an error with DotNetNuke but I'm not sure.  Does anybody know how to programmatically assign someone to a role all the time?  I'm considering putting in a LOOP after this to see if the user IS in the role and if NOT then assign them into the role AGAIN until they are.  I'd rather not code like that since it might end up in a weird loop but....  Here is my code that sometimes works and sometimes doesn't:

CAN ANYBODY TELL ME HOW TO POST CODE SAFELY ON HERE WITHOUT THE formAT GETTING SCREWED UP?  Like a [CODE] [/CODE] method?

 ' Now give role access
Dim TheRoleName As String
Dim TheRoleID As Integer
If RequestInfo.InstructorPilot Then TheRoleName = "AF-IP"
If RequestInfo.StudentPilot Then TheRoleName = "UPTstud"
If (Not RequestInfo.InstructorPilot) And (Not RequestInfo.StudentPilot) Then TheRoleName = "AF-PilotSelect"
Dim RoleController As New DotNetNuke.Security.Roles.RoleController
Dim RoleInfo As New DotNetNuke.Security.Roles.RoleInfo
RoleInfo = RoleController.GetRoleByName(Me.PortalId, TheRoleName)
TheRoleID = RoleInfo.RoleID
RoleController.AddUserRole(Me.PortalId, OurUserID, TheRoleID, Null.NullDate)