[StructLayout(LayoutKind.Sequential)]
private struct DLLVERSIONINFO
{
  public int cbSize;
  public int dwMajorVersion;
  public int dwMinorVersion;
  public int dwBuildNumber;
  public int dwPlatformID;
}

[DllImport("comctl32")]
private static extern int DllGetVersion (
  ref DLLVERSIONINFO pdvi);

[DllImport("kernel32")]
private static extern IntPtr LoadLibrary (
  [MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);

[DllImport("kernel32", SetLastError=true)]
private static extern IntPtr GetProcAddress(IntPtr hModule,
  [MarshalAs(UnmanagedType.LPStr)] string lpProcName);

[DllImport("kernel32", SetLastError=true)]
private static extern IntPtr FreeLibrary(IntPtr hLibModule);

[DllImport("uxtheme")]
private static extern bool IsAppThemed();

[DllImport("uxtheme")]
private static extern bool IsThemeActive();
    

public static bool IsVisualStylesEnabled()
{
  bool retVal = false;
  if (IsThemesSupported())
  {
    IntPtr uxTheme = LoadLibrary("uxtheme.dll");
    if (uxTheme != IntPtr.Zero)
    {
      IntPtr handle = GetProcAddress(uxTheme, "IsThemeActive");
      if (handle == IntPtr.Zero)
      {
        MessageBox.Show(new System.ComponentModel.Win32Exception(
          Marshal.GetLastWin32Error()).Message);
      }
      else
      {
        if (IsThemeActive() && IsAppThemed())
        {
          DLLVERSIONINFO version = new DLLVERSIONINFO();
          version.cbSize = Marshal.SizeOf(version);
          if (DllGetVersion(ref version) == 0)
          {
            if (version.dwMajorVersion > 5) retVal = true;
          }
        }
      }
    }
    FreeLibrary(uxTheme);
  }
  return retVal;
}

public static bool IsThemesSupported()
{
  OperatingSystem os = System.Environment.OSVersion;
  return os.Platform == PlatformID.Win32NT && 
    (((os.Version.Major == 5) && (os.Version.Minor >= 1)) || 
    (os.Version.Major > 5));
}