Actually, I can't find it at all.  There is other software by the same name,
but the home page of NetSpider was on a Zambian server, which now has a
redirect to a new server.  The new server does not have the user directory
"antonia," which appeared to be owned by someone using the name Nikolay Iliev
- the publisher of NetSpider.  I guess NetSpider is no more.

Perhaps other file/graphics downloaders might do the trick.  They tend to be
simpler.  Nevertheless, if you really want to, you should be able to do the
same thing with HTTrack, then delete any html and other files.  Text files
don't take long to download anyway, so if you set your filters to take only
html and gif/jpg files, it should be relatively quick to mirror most sites.

Cheers.