Forget your fancy routers and range extenders.
If you're having trouble getting a decent, reliable connection get this instead. This has, in a single stroke, solved all my connection problems.
This adapter goes in through your USB 2 port, has a hi-gain receiver, and is on a lead - so you can actually place it on your desk, in the right position to receive your modem signal. I'm using it in combination with just my normal modem, and my connection has been absolutely superb ever since.
One small word of caution, though: don't use the wireless utility that comes with the adapter software - as it completely conflicts with the standard Windows network manager. Unfortunately, it installs itself as you load the drivers, so watch out for this. You have to completely close this program off before you can get a good signal.
But all in all, an absolutely brilliant piece of kit.