> WinHTTrack stored all of www.myfriend.com very well,
> but it has also downloaded quite a few (many MB) of
> www.otherguy.net pages, including .htm pages.

Did you change any other options?  Is "Experts Only > Global travel mode" set
to "Stay on same address"?
The default filters (scan rules) will allow all linked images/JS/CSS to be
downloaded from other sites, so it could be that.  If you don't want any of
it, try removing all filters.