Is there really a difference between achievement motivation and affiliation motivation?

Yes. Both kinds of motivation lead people to pursue activities in search of satisfaction of a need, but the focus is different. Need for achievement leads people to pursue activities that allow them to measure their successes. Need for affiliation leads people to pursue activities that foster interpersonal relationships.

Sometimes it seems as if emotions just get in the way. What purpose do they serve?

Emotions serve at least two major functions. First, they provide us with information about a situation. Experiencing fear, for example, warns us that we are in some way threatened, and action must be taken. Happiness gives us the message that everything is OK. With this information, we know how to respond both in the present (run from that oncoming car) and in the future (don't walk in the middle of the road).

Second, emotions provide others with information about us. Because we generally display our emotions verbally and nonverbally, they inform others about our internal states, allowing them to respond appropriately.