Piece of cake. Turns out all versions of Windows use the same networking scheme, so you can share files freely among PCs using different Windows versions.

Once some files are shared (on any PC), here's how to find them:

In Windows Vista: Choose Start->Network.

In Windows XP or Windows Me: Choose Start->My Network Places.

In earlier versions: Double-click the desktop icon called Network Neighborhood or My Network Places.

Now you see icons that correspond to the computers of your network (including your own machine).

If you don't see the Vista computers, it may because all the machines don't have the same workgroup name. (A workgroup is a cluster of networked machines.) To change your Windows XP computer's workgroup name to match, choose Start->Control Panel; click "Performance and Maintenance," and then open System. Click the Computer Name tab, and then select Change.

Or, to change your Vista PC's workgroup name, choose Start->Control Panel; click System and Maintenance; open System. Under the "Computer Name, Domain, and Workgroup Settings" heading, click Change Settings.

Truth is, you can even open Windows machines' icons if you're using Mac OS X. Click the Network icon in your Sidebar, as shown here. Then click the Workgroup folderthat's the standard name for Windows network clusters, although someone may have changed it. Inside, you find your Windows PCs listed, ready to open (assuming you have an account on them).