The following VBA function enumerates all plotters that have corresponding .pc3 files, you can use this in your VBA applications:
Public Function GetPlotters() As Collection
Set GetPlotters = New Collection
Dim strPlotter As String
strPlotter = Dir(Application.Preferences.Files.PrinterConfigPath + "\*.pc3")
While Not strPlotter = ""
GetPlotters.Add strPlotter
strPlotter = Dir
MsgBox strPlotter
Wend
End Function
A method to enumerate system printers (these are also available in the plot dialog of AutoCAD) is available on the following Microsoft knowledge base article: