STEP 1
-click Start > Control Panel > Network and Sharing Center.
-click Change Advanced Sharing Settings.
-make sure File and Printer Sharing is Turned On.
-make sure Password Protected Sharing is Turned Off.
STEP 2 (If that didn't work)
-click Start > type gpedit.msc
-navigate to Computer Configuration/ Windows Settings/ Security Settings/ Local Policies.
-click on User Rights Assignment.
-click "Access this computer from the network"
-make sure EVERYONE is added to the list.
STEP 3 (If that didn't work)
-click here Windows Server 2003 Resource Kit Tools: http://go.microsoft.com/fwlink/?LinkId=4544(ignore message about known issue.)
After installation is complete, click on: Start > All Programs > Windows Resource Kit Tools > Command Shell
Type (Attention: they are case sensitive.)
1.net user guest /active:yes
2.ntrights +r SeNetworkLogonRight -u Guest
3.ntrights -r SeDenyNetworkLogonRight -u Guest
The first command enables network access for Guest, the two subsequent ones change two different policies to allow network access for Guest.