I have a desktop PC (A)connected by ethernet cable to a wireless router. I have a second PC (B) connected wirelessly to the router. Both computers have been assigned IP addresses by the router. Both PCs can successfully access the internet via the router. I want to share files between them. I can ping A from B, but cannot ping B from A. How do I get my 2 computers to recognise each others presence?

What Operating System (OS) are on both computers?
Ensure that both computers are on the same network.
To check this "right" mouse click on "My Computer" and go to "Properties".
The go to computer name and ensure they both say "Workgroup"

Thanks for taking the trouble to respond.

FYI both computers are running Windows XP Pro and were in the same network. I have actually managed to solve the problem now. It was due to the firewall in Norton Internet Security 2007. This was running on both machines. It appears to have been blocking the ping from the wired machine to the wireless one. By disabling the firewall on the wirelessly connected machine (B) it became visible to A and everything seems to be working fine now. Hope this helps anyone else with a similar problem.