Hi Joz, i notice you're running Vista and I believe this may be the problem. Something called wireless zero a configuration that searches for the best access point every few mins or so and causes disconnections.
In Xp there was a way of turning this off, in Vista this is not the case. I had the very same problem as you're describing was insanely annoying in high stakes poker games!! But I managed to fix it just before I bought homeplugs - a good option if this doesn't work.
I downloaded this
http://www.martin-majowski.de/wlanop.../downloads.php try it out. It solved my problems. Or there's another program that's very similar called vista anti-lag. Some people say these work. For me they did. Best of luck, hope this helps.