Is it possible for Macs and PC's to exist on the same network, and share files with each other?

I ask cuz my sister has a 3 pc network with a Netgear DG814 hub at the heart. She is aquiring the 'new' mac G5 in the next few months from her boyfriend. (aww how cute!). Anyway she is wondering if it can be connected to the same network or would it act as a lone computer.

Thanks for any help.