Stan Sted,
Your Mac and PC can both use TCP/IP to communicate to the internet via a shared home network (which is hardware and operating system independent) and broadband router.
Obviously they will need to be configured (each in their own way) to access the network using DHCP or fixed IP address.
What they can't do is talk to each other (e.g. to share files or applications) without installing additional software on one or both computers to allow interaction at an operating system level.
HTH
SD