How to calculate suitable dummy load for a power-supply?
re: Halogen light bulb

Since I'd like to illustrate with a picture, I'm writing this as an answer rather than comment.  This is a response @jippie to his comment to the O.P., which suggests using a light bulb instead of a resistor.

Here's a caveat to be aware of. Resistance of the filament of the light bulb will go up with temperature.  By design, the filament will get quite hot.  This non-linearity is illustrated by this plot:



For more discussion on light bulb resistance, see pp.21-25 here.

re: O.P.

Calculations in the O.P. are correct. 
I concur with @Madmanguruman recommendation about higher power rating for resistors.