I know one way of making multiple computers undetectable: Xforwarding on
the main box for all the apps and user accounts.  As an added bonus, it
keeps all admin on the server and makes cheapo client boxen fast and
diskless even.  I used to do just this over a wireless link for my
neighbors (the COO of the ISP is a good friend and encouraged this at the
time) and worked great (except when it rained.)

Unfortunately, I don't see sharing with neighbors as very ethical or legal
behavior these days.  The novelty has worn thin and it can kill an ISP if
the masses try it.  What used to be fun and a learning experience can now 
be a headache.