In order to be able to see other windows systems from the XP systems you will need to make sure a protocol is loaded on the XP based system. Go to Control Panel, Network Connections the right click on Local Area Connection and then select properties. When the box comes up look through the list for
NWLink IPX/SPX NetBIOS Compatible Transport.
This protocol is what lets two windows systems see each other and communicate. Windows 7 has this installed by default. If it is not listed click the Install button just below the box and select "Protocol" you should see NWLink IPX/SPX in the list. Select it and click OK. It will take a second to load then OK the first screen and reboot the computer.