USERNAME

Returns either the application user name or the network domain name.
For instructions on how to add a function to a workbook refer to the page under Inserting Functions

'sType - The type of username you want to return.

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

Public Function UserName(ByVal sType As String) As String 

Dim sBuffer As String * 255 
Dim lLength As Long 
Dim sUserName As String 

   If (UCase(sType) = "APPLICATION") Then 
      UserName = Application.UserName 
   End If 
   
   If (UCase(sType) = "DOMAIN") Then 
      sUserName = "" 
      lLength = GetUserName(sBuffer, 255) 
      lLength = InStr(1, sBuffer, Chr(0)) 
      If (lLength > 0) Then 
          sUserName = Left(sBuffer, lLength - 1) 
      Else 
          sUserName = sBuffer 
      End If 

      UserName = UCase(Trim(sUserName)) 
    End If 
End Function 

The application username can be seen from the (Tools > Options)(General tab).
The network username can be seen from ..

UserName("Application") = "Russell Proctor"
UserName("Domain") = "proctorr"