Airport - DHCP clash on 3Com Router

I am experiencing strange problems in obtaining an IP address at a
certain wireless hotspot. I'm an iBook user with an Airport Extreme
card, though i'm told any user with an Airport Extreme has this problem
(the site manager of this 'hotspot' is aware of the problem but is baffled).

Although I don't have access to the offending equipment, what I gather
is that it's a 3Com wireless router / access point which dishes out IP
addresses via DHCP to all wireless clients. Users using Windows machines
or even older iBooks with standard Airport cards are able to join the
network without any problems.

Users of newer iBooks / Macs with Airport Extreme cards are presented
with a popup box saying that the IP address given conflicts with another
on the network. No matter what address is chosen (even manually), or how
many times you attempt to obtain a new DHCP lease, the same message appears.

Has anyone come across this problem before?

Terence