Getting windos version code is open for all in MS website itself.
The code is same -there is no other procedure of getting OS version from vb6 other than this.

Public Declare Function GetVersionExA Lib "kernel32" _
               (lpVersionInformation As OSVERSIONINFO) As Integer

Public Type OSVERSIONINFO
               dwOSVersionInfoSize As Long
               dwMajorVersion As Long
               dwMinorVersion As Long
               dwBuildNumber As Long
               dwPlatformId As Long
               szCSDVersion As String * 128
End Type


==========================

Public Function getwinOS() As String
    Dim osinfo As OSVERSIONINFO
               Dim retvalue As Integer

               osinfo.dwOSVersionInfoSize = 148
               osinfo.szCSDVersion = Space$(128)
               retvalue = GetVersionExA(osinfo)

               With osinfo
               Select Case .dwPlatformId

                Case 1
                
                    Select Case .dwMinorVersion
                        Case 0
                            getversion = "Windows 95"
                        Case 10
                            getversion = "Windows 98"
                        Case 90
                            getversion = "Windows Millennium"
                    End Select
    
                Case 2
                    Select Case .dwMajorVersion
                        Case 3
                            getversion = "Windows NT 3.51"
                        Case 4
                            getversion = "Windows NT 4.0"
                        Case 5
                            If .dwMinorVersion = 0 Then
                                getversion = "Windows 2000"
                            Else
                                getversion = "Windows XP"
                            End If
                    End Select
    
                Case Else
                   getversion = "Failed"
                End Select

               End With

getwinOS = UCase(getversion)
End Function