1. When I had 2 comps - there were no any problem, just one twisted pair.
2. No I`ve got 4 comps & had to buy hub/switch, so when I connected RJ-45 with twistedPair and pluged it to Ethernet-card And to swith, the computers doesn`t see each other & doesn`t ping at all.
take care on the cables: for a direct connection it must be a cross-over-cable. But for a connection via hub it must be a 1:1-cable (not crossed). So you can't use the old cable anymore (except if connected to the uplink port - but that's too much for today ...)