i've put your code and worked almost perfect:

[vba]
Private Sub CommandButton3_Click()
Dim vName As Variant
Dim sName As String
Dim sPath As String
Dim sFilter As String
sFilter = "Excel File's (*.xlsm), *.xlsm"
vName = Application.GetSaveAsFilename(, sFilter)
If TypeName(vName) = "Boolean" Then
'user pressed cancel
Else
sName = Right(vName, VBA.Len(vName) - VBA.InStrRev(vName,
Application.PathSeparator))
sPath = VBA.Left(vName, VBA.Len(vName) - VBA.Len(sName))
form_principal.Produto.Value = sName
End If
End Sub
[/vba]

but I wanted the dialog box of the saves as to be in a specified folder
and in the text box appears the extension of the file... just wanted the name... sorry to be a pain in the ass