How do charges move in insulators?

[Justonium]

I'm having trouble understanding one of the most basic electrostatic experiments. When silk is rubbed on glass, the glass apparently acquires a positive charge distributed throughout it, and the silk also acquires an evenly distributed negative charge. How can the charges spread evenly through insulating materials, and also, if they can move around in both the glass and the silk, how can the extra electrons in the silk not be able to move right back over to the glass that is touching it? How does it all work? Also, a website explaining all about electrostatics would be very helpful, as I have been unable to find a good one.

Edited June 16, 2009 by Justonium
correcting a gramatical error

[swansont]

The charges don't distribute themselves throughout an insulator. Charges might collect on the surface, as in the case with the static charge.