Wireless Connection keeps dropping with VISTA

Hi, i've got a BT Homehub Wireless network set up which my Desktop PC
(Windows XP) has quite happily connected to and works flawlessly with. The
problem i've got is that my Dell laptop has Vista installed, and although the
BT helpdesk has been through the setup and config a number of times now, i
cannot get the laptop to stay connected Wirelessly for more than 5 minutes.
Everytime i connect it to the wireless network it works fine for approx 5
minutes then the same thing happens, all of a sudden the status icon changes
to limited connectivity and i lose the Wireless internet connection. I then
have to connect by the ethernet to get onto the internet, unless i reboot the
laptop and go through the whole set up process again.. which will give me
another 5 minutes wireless connection only!!

Can anybody help?
thanks