MAC OS and Win XP file Sharing

I have a home network that has 2 MACs and 2 PC’s. Both MACs are running MAC OS 9. The PC’s are running windows XP and Windows 2000 Professional. I want to share files between these machins over my LAN. How do I set this up. I read somone mention that seting up file sharing betwwen XP and the MACs is easy. I want to be able to do this without making any additional third party purchases. Share the knowlesdge please. Thanks