50% packets dropped connecting PC to ASUS AM604G router

I am in the process of installing a wireless network to connect a number of
PC to the internet via ADSL. I have purchased an ASUS AM604G ADSL2
MOD/ROUTER which I have installed and configured to connect with my ISP
(using an

RJ45

connection). I have installed a ASUS WL-138GV2 54G PCI card in an AMD Athon
4200 64bit PC with an ABIT motherboard. My problem is that if I configure
the router using any form of encryption the PC, whilst able to see the
router is unable to establish any connection. With all encryption disabled,
the PC can establish connection and is able to see the Intenet, but the
performance is awful. Testing the link to the router from the PC using ping,
approximately 50% of the packets are lost.



To date I have tried reseting WINSOCK, and a complete reset of the IP stack
on the PC.



Does anyone have any experience of these wireless devices, or can offer any
suggestions as what to do next.