It depends whether it is a proper mpeg4 or H.264 format video as to whether iTunes will add it. If it's not, you'd need to convert it. There's a no. of apps for osx that can do it. I think you may need QuickTime pro though.

Actually to correct what I said earlier about iTunes automatically adding ... it only does it with music. For videos you need to add them manually. Unless you change something in the LW support files in the prefs folder. I tried it out about a year ago & it worked.