Hmm,unlucky mate.When you say you wacked the bearings in,did you use a big socket,or similar,and drive the bearing in on the outer race?Bearings can get damaged by belting them in the centre.(You probably know that tho!)
Has the ST got one of those conical spacers for the rear wheel,and has it been fitted correctly?Just a thought.
Other than that,get yerself a torque wrench for tightening up the rear wheel.I once helped a guy with a creaking 750SS.Turned out the wheel nuts were that tight,it was the bearings creaking!
Cambelts should be ok for 12k and/or two years.
[Edited on 21-3-2005 by KeefyB]