wireless connection problems under vista

I have a new Packard Bell laptop running Vista. In our house / business we have two other laptops running XP and an xbox all connecting to a wireless network and internet. The Vista laptop regularly loses connection to the network and requires a restart or even sometimes a router restart to reconnect. It can see the network but simply wont connect. The other laptops and the xbox do not have this problem. I have tried a clean install of vista (twice!) and as far as i'm aware have up to date drivers. Router is a buffalo wbmr-g54. Laptop wireless adaptor is built in realtek rtl8187b. Any ideas would be very welcome!