Hope this may help

Private Function GetUserRoles(ByVal web As SPWeb, ByVal Username As String, ByRef sError As String, ByRef isadmin As Boolean) as ArrayList

        ' Retrive the list of Role for the server

        Dim resultArray As New ArrayList



        Dim myws As New WSS.UserGroup





        myws.Url = web.Url.ToString + "/_vti_bin/UserGroup.asmx"

        Dim sUsername As String

        Dim sPassword, sEncPassword As String

        Dim sDomain As String

        Dim sPublicKey As String



        Try

            sUsername = System.Configuration.ConfigurationSettings.AppSettings("usrSiteGroups")

            sPassword = System.Configuration.ConfigurationSettings.AppSettings("pwdSiteGroups")

            sDomain = System.Configuration.ConfigurationSettings.AppSettings("domSiteGroups")





        Catch ex As Exception

            sError = "Error getting sitegroup username, please adjust"

            Exit Function

        End Try

        If sUsername Is Nothing Then

            sError = "Error getting sitegroup username, please adjust"

            Exit Function

        End If

        Dim authorizedCredentials As New CredentialCache

        Dim credentials As NetworkCredential = New NetworkCredential(sUsername, sPassword, sDomain)



        ' Add the NetworkCredential to the CredentialCache.



        Dim sAuth As String = System.Configuration.ConfigurationSettings.AppSettings("auth")



        If sAuth Is Nothing And sAuth = "" Then

            sAuth = "NTLM"

        End If

        authorizedCredentials.Add(New Uri(myws.Url), sAuth, credentials)



        ' Add the CredentialCache to the proxy class credentials.

        myws.Credentials = authorizedCredentials

        Dim ndGroups As XmlNode = myws.GetRoleCollectionFromWeb()



        Try

            For i As Integer = 0 To ndGroups.ChildNodes(0).ChildNodes.Count - 1





                ' For each role list the users, scan thru the user



                Dim onerole As XmlNode = ndGroups.ChildNodes(0).ChildNodes(i)



                Dim RoleName As String = onerole.Attributes("Name").Value

                myws.Credentials = authorizedCredentials



                Dim ndUsers As XmlNode = myws.GetUserCollectionFromRole(RoleName)



                For j As Integer = 0 To ndUsers.ChildNodes(0).ChildNodes.Count - 1



                    Dim oneuser As XmlNode = ndUsers.ChildNodes(0).ChildNodes(j)

                    Dim UserRoleName As String = oneuser.Attributes("LoginName").Value

                    If Username = UserRoleName Then

                        If RoleName = "Administrator" Then

                            isadmin = True

                        End If

                        resultArray.Add(RoleName)

                        Exit For

                    End If

                Next

            Next



        Catch ex As SPException

            Dim message As String = ex.message

        Catch ex As Exception

            Dim message As String = ex.message

        Catch ex As System.Web.Services.Protocols.SoapException

            Dim message As String = ex.message

        End Try

        Return resultArray

        ' For each role, retrieve list of user, if user in the role, add to the list



    End Function