Can't see client or ping, online though.

[digitalpencil]

Hi,
I'm having some trouble with my home network which consists of 5 machines (4 xp, 1 osx) connected to a wireless router.
The machines can all talk to one another accept for one. This is an xp client connected to the correct network with a static IP, correct subnet and workgroup and no running firewall.
The client can ping all machines on the network but none can ping or see it.
If anyone knows of a way of fixing this then please let me know,

All advise is greatly appreciated,
Thanks,
DigiPencil.