SM
From Acapulco take the Autopista del Sol towards Mexico City. After you cross Chilpancingo take the way to Iguala - Zumpango del Rio (I guess is the left lane). That's a two-lane windy road that passes by many small towns. When entering Iguala you will see a detour to Mexico City (to the right). Continue straight to Iguala and follow the Taxco - Periferico (loop road) if you want to avoid the city. In less than 30 minutes you'll be in Taxco. To retun just follow your steps back :-)
There's a second choice: from Chilpancingo continue to Mexico City's detour until you reach the signal to Taxco. (I consider this a longer but better driving conditions if you are not used to drive in Mexico).
M