how do I network windows and mac?

I've an older windows xp laptop that can access internet via my home wifi and of course, my mac family of iMac, macbook pro, iPad, and iPhone can access internet by wifi. The macbook pro and iMac can see each other in Finder.

Problem is, I can't get the iMac nor the win xp laptop to see each other.

How do I setup each to play nicely on the home network?

Thanks! Vince.