I have a wireless network with static DHCP enabled with 3 clients, 2 using WinXP, 1 on Ubuntu
All computers can access Internet fine.
The WinXP computers can share files with each other and ping each other.
The Ubuntu computer cannot even ping the other two. Interestingly, I sent a file from the Ubuntu machine to one of the other computers yesterday so something just happened today.
Also, the Ubuntu machine can only ping itself by IP (192.168.x.x), not by name.
I use Firestarter to manage firewall settings and nothing relevant is being blocked, and if it were blocked, only incoming requests would be affected.
I have tried disabling the software firewalls on the WinXP machines to no avail.