Wireless signal drop during logon

I am having a problem where the wirless connection drops out during a logon
which causes profile corruption.

I have a Dell D600 with XP+SP2 & 2100 truemobile wireless card and am
logging onto a network which uses roaming profiles.

During logon all seems ok, the harddrive is going like the clappers to
suggest the profile is being copied across, yet after 30 secs or so all
activity stops and an error message apprears to tell me that it cannot copy
"file.extennsion to folder".

Last time i logged in i set up a constant ping to the ip address of the
laptop, and sure enough, after 30 or so seconds of disk access it all stops
and the ping replies stop. As soon as i get the error message the laptop
starts to reply to the ping again

I have tried our new hp laptops on the same access point, they logon fine,
tried other 3rd party laptops, they logon fine.

Ive also tried in the dell a dlink pcmcia wireless nic, still the same
problems.

Any ideas please, im kinda loosing patience with these laptops.

Thanks
James