ExtractWindowsUser

'get the correct API
Private Declare PtrSafe Function Get_User_Name Lib "advapi32.dll" _
  Alias "GetUserNameA" (ByVal lpBuffer As String, nSize _
  As Long) As Long

'function declaration
Function ExtractWindowsUser() As String
    'variables
    Dim stringBuffer As String * 100
    Dim longBufferLength As Long

    'set variables
    longBufferLength = 100
    Get_User_Name stringBuffer, longBufferLength

    'get the user's name
    ExtractWindowsUser = Left(stringBuffer, longBufferLength - 1)
End Function