Most golf shops
epoxy
There are two types of golf shaft- Steel and Graphite. Generally steel is used on irons, wedges and putters, whereas graphite is mainly used for drivers and fairway woods. A new type of shaft has recently evolved it is the bi-matrix shaft which is steel and graphite.
Currently Fujikura Blur shaft for 2011 is a mere 47g for their R2 flex model.
Torgue refers to the twisting that happens to the shaft of a club as it is swung. Not only does the shaft of a golf club flex or bend as it is swung but it twists also. A graphite shaft manufacurer that markets a shaft as having low torque for examle, is saying that the shaft is designed to resist twisting as it is swung. The theory being less torque creates a more stable clubhead at impact.
Yes, in principle you can take a shaft out of one club and put it in another. If it's a steel shaft, it's almost certainly cheaper to just replace it with a new one. For graphite it's not beyond the capabilities of a well-equipped shop, but it would still probably be cheaper when it was all over to put a new one in the other clubhead. Unless it was a really special shaft. And I can't define "really special".
The companies that make shafts for golf clubs will have a specification listed on the shaft itself such as "Stiff" of "Juniors". We call it "Flex". The flex standard may be the same on a graphite or steel shaft made by one company and nearly the same as made by another company. It is kind of like sizes for cloths. Both graphite and steel shafts come in "Stiff" flex. Companies may use the word "Mens" in place of "Stiff" or "Juniors" in place of a "not so stiff" shaft. Consult with your local Golf Coach or Golf Professional and they can explain more about the flex in a shaft or other things like "kick points" in a shaft.
Shaft is the handle of the golf club.
Personal preference really. If you are a high or low handicapper say 28- 3 you would hardly be able to tell the difference. Generally, the heavier the shaft, the stiffer it plays. The 60 gram would be whippier, so better suited to a player with a slower swing speed.
You would use golf club epoxy, it is a very strong two part glue.
Driver or Drivers
The lightest driver head in golf is the Vulcan Speedlite V14 driver, weighing in at 185 grams. With the 40 gram grip, and 45 gram shaft, the whole driver weighs 270 grams. The Cleveland XL 270 also weighs 270 grams, but most of it's weight saving is due to it's 39 gram shaft.