Netgear 832G probs with more than one connection

I'm connected via ADSL with a Netgear DG834G router in the UK. Previously I
had the 2 pcs connected via RJ45 and my laptop via wifi. That all worked
perfectly. We wanted to get rid of the 2 network cables so I got 2 Belkin
pci wifi cards to go in both the pcs. Now I'm having trouble. I can find the
wireless connection and my WEP key is accepted ok. 1 system will connect ok.
As soon as another makes a connection, the first one suddenly drops. It
tries to reconnect and gets stuck at the "acquiring network address" stage.
I've tried setting all the pcs to both automatic and manual DNS with the
same results. The router is also running the latest firmware. When I loose
the connection and I plug in my old RJ45 cable, i'm fully connected in less
than a second. What the hell's going on?

Forgot to mention, the 2 pci cards in the desktop pcs are both Belkin
F5D7000UK. Although the problem also affects the laptop with has been
working perfectly since January on wireless.