Problems with Intel PRO LAN 2100 3B

I have a new Fujitsu Siemens Lifebook E4010 running Windows 2000 Pro
and I'm having wireless problems with the (built-in) Intel PRO LAN
2100 3B.

The wireless network seems to operate OK but when surfing the 'net it
stalls sometimes. ICQ keeps disconnecting and reconnecting every few
minutes and intermittently drops messages. Ping times from other
computers in the house show a wide range of round-trip times - between
2 and 200 ms.

There are no problems if the Lifebook is plugged directly into my
ethernet switch. My older laptop (IBM ThinkPad with Avaya PCMCIA
Wireless card) functions just fine (no dropouts, ping times
consistently about 2ms) so I don't think I have any problems with my
access point (Linksys WAP11 with latest firmware). The Lifebook works
fine with the Avaya card too.

I'm currently using driver version 1.0.28.2 (January 2003) and thought
new drivers might be in order but where do I download them from? The
Intel site tells me to visit the hardware manufacturer. The Fujitsi
Siemens website tells me that the product is licensed and that I
should have a copy on one of the CDs which came with the machine.
Indeed I do - but the same version as the one already installed.

Anyone any ideas as to the cause of the problem, whether new firmware
for the Intel 2100 would help and if so, where do I obtain it?

TIA

Steve T.