'--- Letakkan di module
Public Declare Function GetUserNameA Lib "advapi32.dll" _
   (ByVal lpBuffer As String, nSize As Long) As Long
'--- Akhir Letakkan di module

Public Function GetUserName() As String
   Dim UserName As String * 255
   Call GetUserNameA(UserName, 255)
   GetUserName = Left$(UserName, InStr(UserName, Chr$(0)) - 1)
End Function

Private Sub Form_Load()
   MsgBox GetUserName
End Sub