I've never been in a qualifying race... how do they decide on the starting grid for a qualifier?

I would be concerned about the possibiity of other drivers making bonehead race moves during the quilifier and causing accidents.. just to get a better spot on the grid. (example would be the ITB Volvo at VIR that had "brake problems", yet bonzaid 1, t-boneing an ITA car.

I would rather have a 25 or 30 min qualifier, as opposed to having a 10-15 min practiece and 10-15 min qualifier.