Mike, you don't have to buy shoes to get the Silica gel. Just ask the salesperson to put some aside for you.
To dry the Silica gel simply place in a normal oven that is still warm, and leave o/nite. Some of the bags have a 'polymer' coating on the inside as moisture proofing.
I would not recommend a microwave. You'll break/crack all the granules by heating it too quickly.
As vermin has said, the gel has a colour indicator.
Tony, I have lots here if you want to buy some.
Another source is, any Business Machine Co. eg; CANON,Ubix,Minolta, copier/fax/printer etc etc. They will have heaps of it lying around. HTH.
L.