Windows networking is built into OS X-you just have to turn it on through Preferences. But you ALSO have to make sure that the files on the Windows machine are shared. You share a folder on Windows by right-clicking on the folder in Explorer and selecting Sharing and Security and giving the folder a name to be shared under.
You may run into problems with the Windows machine if it's using "simple file sharing" That should be called "simply not sharing," because it tends to make it nearly impossible to share files. Here's the weird part-you change this setting by clicking on the Tools menu item and then selecting Folder Options...then choosing the View tab. Scroll to the very bottom of the options listed and unselect "use simple file sharing" option.