Dealing with a "know-it-all" co-worker?

I work in a small business office with my boss (who is there every now and then) and two other women. One woman I absolutely love working with, but the other is very arrogant, y, and acts like she "knows it all" She is very rude to me, and expects me to do a lot of her work for her. The problem is, the woman that I like working with has been at this job for 25 years and doesn't want to deal with her. So she stays quiet about the situation. She doesn't want to get involved. Also, my boss likes this overbearing woman who is driving me mad. She likes her so much in fact that she just bought her a company car to drive around and pays her a hefty salary. I know this woman just brown-noses to get everything she wants. I'm afraid if I tell my boss how I feel, then she may look down on me or fire me because she "likes" this other woman better. This woman takes credit for a lot of the work I do, and noses through my stuff like she wants to catch me doing something wrong...