Thanks for the tips. I downloaded Netstumbler and at the moment (while my connection is working) there are 2 other networks available - they are using channel 1 & 11 and I am using 9. It will be interesting to see what it looks like when I have a problem.
Brewster - your problem sounds different to mine. The signal strength is fine, and Windows repair doesn't fix my connectivity - it says it can't connect to the network. If I shut down my PC (not a laptop) the connection is cut and I have to reconnect at startup.