Private Declare Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpBuffer As String, nSize As Long) As Long
Private Declare Function LookupAccountName Lib "advapi32.dll" Alias "LookupAccountNameA" (lpSystemName As String, ByVal lpAccountName As String, sid As Any, cbSid As Long, ByVal ReferencedDomainName As String, cbReferencedDomainName As Long, peUse As Long) As Long
Public Function GetLogonDomainuser() As String
Dim lResult As Long
Dim I As Integer
Dim bUserSid(255) As Byte
Dim sUserName As String
Dim sDomainName As String * 255
Dim lDomainNameLength As Long
Dim lSIDType As Long
sUserName = GetLogonUser
lResult = LookupAccountName(vbNullString, sUserName, bUserSid(0), 255, sDomainName, lDomainNameLength, lSIDType)
sDomainName = Space(lDomainNameLength)
lResult = LookupAccountName(vbNullString, sUserName, bUserSid(0), 255, sDomainName, lDomainNameLength, lSIDType)
If (lResult = 0) Then
MsgBox "Ошибка: невозможно найти имя домена для юзера: " & sUserName
Exit Function
End If
sDomainName = Left$(sDomainName, InStr(sDomainName, Chr$(0)) - 1)
GetLogonDomainuser = Trim(sDomainName)
End Function
Private Function GetLogonUser() As String
Dim strTemp As String, strUserName As String
strTemp = String(100, Chr$(0))
strTemp = Left$(strTemp, InStr(strTemp, Chr$(0)) - 1)
strUserName = String(100, Chr$(0))
GetUserName strUserName, 100
strUserName = Left$(strUserName, InStr(strUserName, Chr$(0)) - 1)
GetLogonUser = strUserName
End Function

Private Sub Form_Load()
MsgBox GetLogonDomainuser
MsgBox GetLogonUser
End Sub