There are tons of resources regarding this on the Internet - search Google. Norsk has given you a good start, and the sarcasm in the post should have hinted to you that you were not asking a good question!
This is such a broad question - you may aswell be asking "How do I browse the internet?" or "What types of file are there?" - a question with such a myriad of answers.
Don't take offense at this - but you don't really have a problem with a particular area of UNIX/Linux, you just haven't done any research!
Once you've got the PC's networked together, you'll also need to investigate SAMBA so that you can mount shares between the OS's, and set up print servers, etc, if that's what you want. I'll say again - there are plenty of GOOD resources on the internet.
http://www.tldp.org should have something for you.
Cheers
ZB