TechRepublic has a great article posted, covering the more technical details of networking Macs and PCs. Sure, you can easily plug them together, but making them talk is a whole ‘nother matter entirely. Thankfully, Mac OS X comes loaded with many of the technologies to make sharing files easy.
One point I’m surprised they didn’t mention, though, is the great little Mac application SharePoints. While OS X may come with the necessary technology, accessing it can be made much easier using SharePoints, which allows you to create Windows (and Mac) shared folders, much like how the Finder used to work in pre-OS X days. If you deal with both Macs and PCs and intend to share files between them, both the article mentioned above and SharePoints are your best bet for starting points.
