I needed a good way to get the groups for an active directory user, but in vb.net everything I saw was not quite what I needed or was in c# so I looked at an article available on MSDN, which is in c# and took out what I needed to get the groups for a certain user. There is one catch it will not return anything if there is not a "memberOf" attribute for a user. It actually errors out. so for this they are still a valid user they just are not in any other groups besides the "primary" group in AD so in the catch you can catch this and put in some code to handle these users. 

Setup:

1. In IIS go into Security and instead of using the default IIS username and password you have to add a valid username and password.

2. Add a reference to System.DirectoryServices and at the top of the codebehind add "Imports System.DirectoryServices" 

Code:  

Private Sub Page_Load(ByVal sender As System.Object, ByVal e _
    As System.EventArgs) Handles MyBase.Load
    Response.Write(GetGroups("LDAP://domainname", "username", "password"))
    'Returns String of: "Group1|Group2|Group3|"
End Sub
   
Private Function GetGroups(ByVal _path As String, ByVal _
     username As String, ByVal password As String) As String
    Dim GroupString As String
    Dim myDE As New System.DirectoryServices.DirectoryEntry(_path, _
      username, password)     

    Dim mySearcher As New DirectorySearcher(myDE)

    mySearcher.Filter = "sAMAccountName=" & username
    mySearcher.PropertiesToLoad.Add("memberOf")
    Dim propertyCount As Integer

    Try

        Dim myresult As SearchResult = mySearcher.FindOne()
        propertyCount = myresult.Properties("memberOf").Count
          
        Dim dn As String
        Dim equalsIndex, commaIndex As String

        For i As Integer = 0 To propertyCount - 1
            dn = myresult.Properties("memberOf")(i)
            equalsIndex = dn.IndexOf("=", 1)
            commaIndex = dn.IndexOf(",", 1)
            If equalsIndex = -1 Then
                Return Nothing
            End If

            GroupString += dn.Substring((equalsIndex + 1), _
              (commaIndex - equalsIndex) - 1) & "|"

        Next
        Return GroupString

    Catch ex As Exception
        If ex.GetType Is GetType(System.NullReferenceException) Then
            Response.Write("does not have a group")

            'they are still a good user just does not
            'have a "memberOf" attribute so it errors out.
            'code to do something else here if you want
        Else
            Response.Write(ex.Message.ToString & ex.ToString)
        End If 
    End Try 

 End Function