Here's a thermodynamic explanation of why salt raises the boiling point of water.
Water boiling at its boiling point is a reversible reaction. For a reversible reaction, ?G = 0. Therefore:
?G = ?H - T?S = 0
where ?H is the change in enthalpy of vaporization, ?S is the change in entropy of vaporization, and T is the boiling point. Rearranging this expression, we get:
T = ?H / ?S
Now, when we add salt to pure water, we increase the entropy of the liquid water. Since adding salt does nothing to the entropy of the gaseous water, ?S = Svapor - Sliquid is lower. Since ?H is not changed significantly, the decrease in ?S will increase T (the boiling point of water).