Optimize Windows XP and Windows 7 for file sharing

Click on the "Start" menu and in the "Run" line type "Regedit" and hit Enter.
Navigate to the following location:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\LargeSystemCache
The default value of the LargeSystemCache key is "0" (zero). Highlight "LargeSystemCache" and right click it. From the menu select "Modify".
In the new window change the value data from "0" to "1" (one) and click OK.
Next, locate the following key in the registry:
HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\Size
By default the "Size" value will be set to "0" or "1". Follow the procedure outlined above to modify the value and change it to "3".
Once you have updated these values close the Registry Editor and reboot the system for the new settings to take effect.
The changes we've made to the registry should resolve the Event ID 2017 and 2021 errors and Source Srv/Lanman errors in the Windows Event Log. This will ensure that shared files and folders remain accessible to network users without the need to reboot the system. This should also keep mapped network drives from disappearing as well as optimize overall network performance of the file server.
For more info read the following article