Do you know the Network name of your Netbook?
Right Click on My Computer
Click the Computer Name tab.
If you have My Computer on the desktop of the Netbook, right click on that and choose properties. Same deal.
At any rate, from there, make sure that both computers are in the same Workgroup. Note the Full Computer Name of the netbook.
Now. Open up Windows Explorer on the desktop. You know... Open My Computer, or what-have-you. In the address bar, type "\ComputerName" without the quotes, and where I typed ComputerName, you type the ACTUAL computer name of your netbook... and hit enter. If you have properly set the netbook up for sharing properly, any and all directories that you have designated for sharing will be listed there.
I don't know if you have followed these steps or not. There is no way I can know specifically what you have done, or how much experience you have with XP and such.
The Windows Firewall on the Netbook could be on and it might not be set to allow an exception for File and Printer Sharing. So... go into the Control Panel, Open up Windows Firewall, and click the Exceptions tab. See if File and Printer Sharing is there and checked off. It should be, as it is installed AND turned on by default. However, turn off the Windows Firewall and see if you can access files on the Netbook with the Firewall off.
If you have any OTHER Firewall installed on the Netbook... like one that comes with McAfee or Norton or AVG or Zone Alarm, that could be the issue as well.