I have a BT Voyager 2000 adsl modem/router connected to an iMac with
an Airport Extremem card and to a Vaio running XP Home and connected
by a BT Voyager 1020 PCMCIA card.

The firewall is set of OFF and I have 128 bit WEP enabled.

The download speed varies from OK (never as fast as would be expected)
to extremely slow. Signal strength is always OK (distance is only
about 15 feet).

If I connect either machine to the 2000 with an Ethernet cable
everything works at excellent speeds.

Can anyone offer any advice?

Thanks