Rookie question, can a mac communicate with a pc over a home network, or are they completely different animals. I have 3 computers on my network (1 HP and 2 Dells) and have been thinking about Apple.

Communication itself is TCP/IP just like anything else (Empegs, TiVos, unusually smart toasters).. Apple has their own file sharing protocol (AFP) but OS X is just as happy speaking in Microsoft's (SMB).