Spraying a lube, oil or WD40 is not a good idea, and will not do anything to improve your squeeking belt! Spraying oils etc will infact only wear out / damage the rubber.
If anything can be done it is this:-
1/ shake some good old talc powder over the belt whilst it is running, ensuring it makes contact with the inside edges of where belt meets the surface of the pulley. It won't solve it indefinately, but it will stop it until you can get another one fitted ASAP. All it does it breaks up between the two shinney surfaces of the belt and pulley reducing the level of friction noise caused by a worn belt!
2/ The edges of the belt are worn / shiney causing friction against the naturally shiney metal surface of the pulley. Simply replace the belt for a NEW one and be done with the spueek once and for all!
Kent
January 2009