You can try running the Network Wizard, but disregard any reference to transferring files to another computer by Floppy or USB Flash drive - it isn't necessary.
I've "networked" computers many times and never yet used the wizard to do it. Some of the options in the wizard are confusing and it's too easy to select the wrong option.
As your computers are all connected to your router for their internet access, they are already "networked". Set any folders that you want to have available over the network as "shared" by right clicking and selecting the Sharing & Security option [XP] or Share [Vista].
In Vista, go into the Network & Sharing Center and set to On:
- Network Discovery
- File Sharing
- Public Folder Sharing
It can also be helpful in the XP PCs to install the Link Layer Topology Discovery (LLTD) Responder click here
Any third-party software, such as Zone Alarm, needs to be configured to allow access to the networked computers, which may involve adding their IP addresses in a "trusted" section.
For instructions on setting up a "shared" printer (attached to an XP PC) in Vista click here