See above re astolat's instructions -- the "direct stream copy" option in Vdub does *nothing* to compress your video -- that's why you are ending up with files of the same size. It's useful if you need to clip parts of a file without losing quality, but that's it. You need to use "full processing" mode.

(IMO, converting to .wmv is a bad choice. Use a .dv codec, like the Panasonic one, instead.)