Yeah, CCCP leans very heavily on ffdshow (which is just a directshow filter, not a vfw codec) for its decoding. So if you're doing virtualdub work, you need to actually install compatible vfw codecs (ie: koepi xvid binaries).

To be honest, if you're working with vdub, you probably aren't well-served by cccp anyway. You'd be better served by the Gordian Knot codec pack -- which really is an encoder's codec pack.

Most other things are really more playback-centric, and CCCP is no exception.