Below is a code snippet that allows you to determine what groups a Windows user is part of.

[C#]

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Principal;
using System.Text;

namespace KeithRull.ActiveDirectory.IdentifyingUserGroups
{
    class Program
    {
        static void Main(string[] args)
        {
            //get the WindowsIdentity of the current user
            WindowsIdentity currentWindowsIdentity = WindowsIdentity.GetCurrent();
            //retrieve the groups that the user belongs to
            IdentityReferenceCollection currentWindowsIdentityGroups = currentWindowsIdentity.Groups;
            //iterate thru each group
            foreach (IdentityReference identity in currentWindowsIdentityGroups)
            {
                //translate the identity into an NTAccount identity
                IdentityReference ntAccountIdentityReference = identity.Translate(typeof(NTAccount));
                //get the value
                string groupName = ntAccountIdentityReference.ToString();
                //print to console
                Console.WriteLine(groupName);
            }
            //pause
            Console.ReadLine();
        }
    }
}

[VB.NET]

Imports System 
Imports System.Collections.Generic 
Imports System.Linq 
Imports System.Security.Principal 
Imports System.Text 

Namespace KeithRull.ActiveDirectory.IdentifyingUserGroups 
    Class Program 
        Private Shared Sub Main(ByVal args As String()) 
            'get the WindowsIdentity of the current user 
            Dim currentWindowsIdentity As WindowsIdentity = WindowsIdentity.GetCurrent() 
            'retrieve the groups that the user belongs to 
            Dim currentWindowsIdentityGroups As IdentityReferenceCollection = currentWindowsIdentity.Groups 
            'iterate thru each group 
            For Each identity As IdentityReference In currentWindowsIdentityGroups 
                'translate the identity into an NTAccount identity 
                Dim ntAccountIdentityReference As IdentityReference = identity.Translate(GetType(NTAccount)) 
                'get the value 
                Dim groupName As String = ntAccountIdentityReference.ToString() 
                'print to console 
                Console.WriteLine(groupName) 
            Next 
            'pause 
            Console.ReadLine() 
        End Sub 
    End Class 
End Namespace 

HTH