VirtualDub filters may be run in a couple of alternate execution environments other than VirtualDub itself.  Here are a few you should be aware of:

Avisynth
Avisynth 1.0 beta has the capability of loading VirtualDub filters via its LoadVirtualdubPlugin command.  Avisynth's support for the VirtualDub filter API is somewhat limited to the basics, so you must be careful if you want to maintain compatibility.  Avisynth compatibility warnings are included throughout this documentation.

VirtualDub 2.0 (Nina)
Nina is currently in development and contains a filtering system which is very different than the one described here.  It is thus expected that filters which are designed for the V1.4x interface will run in an emulation layer.  This emulation layer has not yet been written, but warnings have been included for features which are likely to run poorly in the emulation layer.