The converting from .2d to DXF is accomplished by an external program called vlink (with a DOS command-line interface) It could be automated via a Batch file or something like winbatch.
Also, versacad has been "windowized" and comes with a nice translation utility - an "external" windows application, that can 'mass' convert from .2d to dwg directly. Checkout VersaCAD 2003/2004 - might be worth it for that many drawings.
JimL