MacBook Air - cannot connect to any wifi networks!

Ive tried everything from this page and still my MacBook air (i5 core) refuses to connect to any wireless networks other than my iPhone tether. I bought it in the US andwas wondering whether there we're any other suggestions.

I'm running 10.7.3 and my router is the BT homehub 2 (sigh). I also have a d-link router and every other device in the house can see it and connect other than the air.

Any advice? Its like carrying a (light) brick!