Sub MyName()
    Dim CurrentUserName As String
        CurrentUserName = Environ("Username")
    MsgBox CurrentUserName
End Sub

Declare Function GetUserName Lib "advapi32.dll" Alias _ "GetUserNameA" _
(ByVal lpBuffer As String, nSize As Long) As Long

Function UserName() As String
Dim Buffer As String * 100
Dim BuffLen As Long
BuffLen = 100
GetUserName Buffer, BuffLen
UserName = Left(Buffer, BuffLen - 1)
End Function

Private Sub Workbook_BeforeSave _
(ByVal SaveAsUI As Boolean, Cancel As Boolean)
With ActiveSheets
       .Range("a1") = UserName()
       .Range("B1") = Now
End With
End Sub