If you are only hiking to the ruins and back, you can make it without a map. (We did manage to get lost in the maze of trails exiting Cachora.)
There is no good trekking map for the longer routes past the ruins, so far as we know. We feel you should hire a guide / arriero for those treks. In addition, you should confirm the best route with locals & with guides from other groups while on the trail. Conversational Spanish is a big advantage.
The best of the poor maps is IGN 1:100,000 machupicchu map (sheet 2344, 27-q) but it does not have the trails marked on it.
Buy that map (when you get to Cuzco) from the South American Explorers Club. Occasionally they run out. You can also find it in some of the shops in the town centre.
You may want to consult online maps (they open in another window) while planning your hike:
