Yep, just so all versions available if required for whatever reason.
I thought that VirtualDub.org was down some time ago, but is now up:-
http://www.virtualdub.org/
(I'm sure that you already knew that).
and all pre v1.20 filter SDK's also available here:-
http://www.virtualdub.org/filtersdk.html
EDIT: Arh, forums are down though.