As you've got OSX 10.7.3 (the latest version of Lion), it should find the "shared" folders in the Windows PCs without you having to do anything additional. In Finder's menu, just select "Go > Network" and it should find the Windows PCs. To Share the Mac's folders go into System Preferences then, in the Internet & Wireless section, click the Sharing icon and tick File Sharing and Printer Sharing. To share a particular folder, right click and "Get Info" then tick the box to share the folder.
I have only ever done it the other way round - a printer connected to a Windows PC and shared so the Mac can use it. If you need an address, presumably you could use the Mac's IP address, although you might have to allocate a fixed address.
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