You need to first work out if the problem is your router losing connection to the BT network or if your wireless connection to the router is failing.
If you take a look at your wireless adapter IP Protocol settings and make a note of your "default gateway" - this is the address of the router.
Next time you lose connectivity run the ping command using the gateway address as a parameter. So if your gateway is on 192.168.1.1 you would go:
Start Menu, Run, ping 192.168.1.1 -t
If you get a ping response then your router and pc are talking ok - wireless is fine and likely your router has indeed lost its connection to the BT network.
If you get no response then your wireless is playing up.
Hope this helps.