MAXScript for Autodesk VIZ includes a function for DWG link file access.
Its form is:
linkFile <filename_string> [#noPrompt]
This method attaches and links the named .DWG file and returns a value of true if the file was attached and linked, false otherwise. This method is equivalent to Menu bar > Insert > Linked DWG... in VIZ. The optional #noPrompt argument provides control over the display of the DWG Link Options dialog. This method is available only to VIZ users.
External File Methods
File Name Parsing
Standard Open and Save File Dialogs