>Thanks, Igor!
>
>I got an error message: function is not defined.
>Should I add some library files like advapi32.dll?
>
>Natasha

The following works for me on VB6:

'General Declarations on module:
Public gsUserID As String
Private Declare Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" _
   (ByVal lpBuffer As String, nSize As Long) As Long

Public Sub Main()
   gsUserID = GetUserID
End Sub

Public Function GetUserID() As String
   Dim gunReturn As Long
   Dim lpBuffer As String * 255
   Dim nSize As Long
   nSize = 255
   gunReturn = GetUserName(lpBuffer, nSize)
   Dim UserName As String
   UserName = Mid(lpBuffer, 1, nSize - 1)
   GetUserID = UserName
End Function

Note that Sub Main() has been largely simplified to show only the calling syntax.
HTH