wifi ap express & 3rd party wireless adaptor

[YeahButNoButYeah]

Hi collective genius of this great forum,

I've got a G5 that i need to hook up to the internet (dsl modem) wirelessly via an airport express, so i bought an addlogix USB wireless adaptor. It's a bit clunky but seems to work ok, EXCEPT if another particular computer is on in the house. The other computer is an ibook g4 with built-in airport. As soon as it is turned on my connection drops and I cant reconnect until its turned off. I've also noticed this behaviour if someone in the neighbourhood turns on their wireless.

Part of the reason for getting my g5 wirelessed is so I can network it to the ibook, so it's particularly frustrating.

I noticed that the other wireless in the neighbourhood is on the same channel as us, so I've changed ours to a different channel. That seems to have fixed that aspect, but this other problem remains. When the ibook is not on, I get 54% signal strength, 95% signal quality, 36mbps tx rate.

When the ibook is turned on (in another part of the house), I'll get 100% crc reception errors and a dropped link.

Is there something I'm doing wrong in the setup, either of the airport express or this addlogix thing?

The Addlogix adapter is configured thus:
802.11b/g mixed mode
auto 11 b/g protection
auto tx rate
enable tx burst off

The airport is configured as an infrastructure type network (not ad hoc) with wep encryption and open authentication.

Hope that's enough information for someone to help.

Terry