I assume (hope) that the guy above meant to say that you should disconnect the NEGATIVE connector on the battery.
All modern cars are 'negative earth', which means that the metal of the bodywork is connected to the negative pole of the battery.
If you disconnect the positive connector, and something accidentally touches the positive terminal and any part of the bodywork (if you dropped a tool for instance) then it would short out the battery, which is very dangerous!
james
May 2008