XP Clients not connecting to Win 7 after a few days

Tell Windows that you want to use the machine as a file server and that it should allocate resources accordingly:

Set the following registry key to ’1′:

HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\LargeSystemCache

and set the following registry key to ’3′:

HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\Size