Homeplugs to the rescue
Just thought I'd post my experiences for anyone else strugging to get a wifi signal.
I'd been having problems getting a good wireless signal in my conservatory, where my hifi is. I have an airport express in there, for when I just want access to all my music, and am not too bothered about quality. But the signal is poor, because of the distance from my router, and the fact that it has to travel through steel and other things that cause interference (cordless phones, etc). Even a wireless extender didn't fully solve the problem, as the signal always seemed to fail eventually, and that would be the end of the music.
Then recently, I heard about homeplugs. For £40 for a pair on Amazon, I thought they'd be worth a go, and they definitely have been worth it. I am now getting constant, uninterrupted music, and all my problems are finally solved. Delighted.
So give these little beauties a go if you're struggling to get a good signal somewhere in your house.