A wing is a wing is a wing. And lift is all about tilt. More specifically, angle of attack.
Looking at the side of the plane and a cross section of the wing.
The darker line represents the angle of the fuselage - in the top image, parallel with the earth. See how the wing is tilted up slightly. From memory it is about 13 degrees. In the bottom image the plane has gone up, up, up and over and is now flying upside down the way it came. The top of the plane is now nearest the earth. As Maalie predicted, the pilot doesn't fly straight and level, but angles the plane (the controls think downwards, which is now upwards) so that the wing still has that angle of attack. In fighter planes, which require all sorts of manaeuovres, the angle of attack would be negligible, so that the pilot doesn't have to seriosly tilt the aircraft to get it to fly upside down - but as long as the fuel system can cope, any plane can use this method and fly upside down. In fact I have a video of a Boeing 707 doing a barrel roll VERY IMPRESSIVE!!! But I don't think I can load videos onto the blog. If anyone wants to host it for me...!
I hope this helps you 'W.'