CardBus 802.11 card

I'm having problems with an 802.11b wireless card bus,
which is giving very different link performance in 2
(almost) identical Compaq Presario 2100 notebooks. They
differ only by the processor installed. In one notebook,
the cardbus gives a fairly robust wireless link throughout
my house (a fairly standard 4 bedroom N. American home),
with a reasonably constant data rate (as indicated by the
link monitor utility). In the other, the data rate is very
variable and degrades rapidly as I move away from the
wireless router. I note that the IRQ assignment is
different between the 2 notebooks (in the "good notebook"
the cardbus controller and cardbus adapter share IRQ11 with
an IEEE 1394 Host Controller, in the other they share IRQ11
with a 10/100 PCI Adapter). Is this a cause of the
problem? If not, can anyone help?

Thanks