Can't ping between Wired and Wireless PC

I currently have my PC connected to a Thomson 580 router via an RJ45
cable.

I came up with the bright idea of fitting a Wireless interface onto a
low spec Compaq that I have so that I could control my Main PC using
remote desktop or VNC.

In principal it should work.. So, I bought a cheap Linksys WUSB11v4 and
set it up.

Its a bit slow at getting connected, but when its there, the wireless
side seems to be OK, in that I can connect to the internet.. But to my
surprise, the 2 PCs are having problems talking to each other on the
'Intranet' side.

My setup is this

PC (10.0.0.1)
|
cable
|
ROUTER -------> Internet
|
wireless
|
PC (10.0.0.2)

Please note that the addresses have been allocated by DHCP and since
the router has been configured by my work, I can't change it.


>From 10.0.0.1 I can connect to the Internet, but can NOT ping 10.0.0.2
(No Reply)

>From 10.0.0.2 I can also connect to the Internet and CAN ping the
10.0.0.1


Whats strange is that when I first set it up, I could ping between
them, but only intermmittently.. Now that I have been 'fiddling', I can
get from .2 to .1 100% of the time as if it were hard wired, but NEVER
from .1 to .2

Does anyone know where I can start to debug/fix this... I have tried
everything and have run out of patience.

I will take my Laptop home tonight (Which has inbuilt wireless) and
will see what happens if I have 3 devices (2xwireless 1xcabled).. This
will hopefull show whether the problem is with the Router or PC..But my
gut feel is that the Compaq/WUSB11 is to blame!

Jon

PS. I have no FIrewall software installed/enabled on either PC, so its
not a firewall issue!