An ADSL will not work properly with a cable connection you need a cable router of which there are plenty of good ones
to the forum btw if money is no object buy the most expensive with good reviews I do not believe in cutting back when it comes to finances
Edit I have a theory about using a dsl router as a switch so maybe you could test it for me
try plugging the router into you main pc then connect all other to router however you do it . Safely set system restore points on all machines and run network connection wizard on main pc setting it up to have all other pcs connecting to the net throught its connection then run connection wizard on other machines and say you connect through another computer on the network. this in my theory (untested as I say) will set up a ad hoc network maybe