Limiting specific computer access to a network

I have a home office network with a main PC (Vista) and a laptop (XP) which share files and an internet connection via a Netgear WGR614 v6 router. All worked well until my eldest son bought himself a laptop with Windows 7. I wanted to give him access to the internet via the wireless network - but not to be able to read or file share with files on the main PC or the XP laptop.

I tried renaming the Workgroup on the main PC and XP laptop - but his Windows 7 laptop still seems to be able to access the shared files on both of the other computers.

I have since tried using the 'Deny access to this computer from the network' on the main PC, but I get an error when I try to add his laptop name to the list and the database won't update.

How do I still allow him to continue with his internet access but prevent him accessing the business files (whether by accident or intentional curiosity) on bit the Vista PC and XP laptop (while still allowing normal sharing bewteen the Vista PC and XP laptop)?

Go to Network and Sharing Center on the Vista machine. There, enable password-protected sharing. Now, you will require the administrator username and its password to access any folder on that PC. I am not sure about Windows XP, but try the Properties on the shared folder(s) on that laptop. There surely must be something.