I just did this, great project.
Try that tutorial Kowaru posted, that's the same one I used it's very easy to follow.
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Also, if you (or anyone who finds this thread in a future search) want a quick-and-dirty solution, your old Windows box has built in webdav through IIS. This is what I did for a long time until I set it up on the apache server. You don't get the bells and whistles, but it's an excellent way to have your home PC act as a file server between multiple macs:
link . (link also has webdav instructions for OS X and Linux)
However you set it up, be sure to lock down your server when all is said and done.