Re: What is the difference between need and drive?

Yes, you are correct. In standard terminology, "need" is a physiological 
situation that must be resolved (hunger, thirst, etc.).  In such situations, 
the "drive" is the motivation to solve the physiological need.  There are also 
other physiological "needs" such as the infant's need to be loved, stroked, 
held and touched, so do not assume that all needs are strictly from biological 
processes or due to nutritional needs only.

Human beings also have the "higher ape" needs for social interactions, 
hierarchical behaviors, competition, survival, etc. and these are also "needs" 
such as the need to socialize with others.  These also are satisfied by 
various "drives" (motivations to take action in regard to satisfying those 
needs). There is a need for affiliation with other human beings, and a drive 
for human interactions.

As for your examples of "need for achievement," or "need for power," those are 
actually examples of "drives" toward the "need" for survival in an 
interpersonal and social context, so the appropriate term would be "drive" in 
such instances, as in the "drive for success."