If the two computers have internet access via the router, then they are already "networked". You should set any folders that you want to have available over the network as "Shared" by right clicking them and selecting the Sharing & Security option. In any case, at least one folder in each PC should be set as "Shared". Any Firewall software needs to be configured to allow access to the networked computers.
That basically should be it, although to access files in XP Pro, you may have to be logged into the 'client' PC with a Username/Password that matches an Account set up in the XP PC. More about that at click here
This is my standard "blurb" on network printing:
1) Connect the printer to the “client” PC, as though it were to be used with that computer, and install it. This ensures that it has all the necessary software/drivers on board.
2) Reconnect it to the "host" PC and, in its Properties, set it as "shared". In the client’s "My Network Places", the printer should then appear as a shared resource of the "host" PC along with any shared folders. Double clicking the printer in the remote PC should automatically install it as a "network printer" in the “client”. This means that the “client” now has the same printer installed twice – once as a “local” printer and again as a “network” printer (with a bar under the icon to indicate a network device).
Otherwise, have a look at this Microsoft article. It is an old article written for Windows 95, but the basic principle for installing the network printer should still be valid.
h t t p : / / support.microsoft.com/default.aspx?scid=kb;en-us;141839