Users have reported a variety of local networking issues under Windows 7. These include an inability to see or exchange files with Windows Vista or XP systems, inability of other systems on the LAN to see Windows 7 systems and more.
Some networking issues may be related to mismatched authentication settings. Make sure that local area network authentication settings are the same on all computers on the network. To check this setting on, click the start button, then entersecpol.msc in the search field (use “Run:” in Windows XP) and press enter.
Navigate to Local Policies > Security Options and find “Network Security: LAN Manager authentication level.”. Make sure it carries the same settings on all systems and the server, if one exists.
Some users have also had success with temporarily turning off the Windows 7 firewall, allowing other machines on the network to be discovered, then turning the firewall back on.
To turn the firewall on or off, open the Control Panel then the click the Windows Firewall icon and modify the setting on the left.