.dv is two streams of data, audio and video, theres a bit of difference how the stream is named in the avi wrapper...
type1 requires a bit less overhead
type2 is compatable with Video for Windows (VfW)
type2 is moreoften compatable with external programs for me.
you could get the long version here
http://www.microsoft.com/whdc/archive/dvavi.mspx