I think that everyone's familiar with the meaning of reincarnation, but in Hinduism and other religions that originated in India, reincarnation is tied to karma, which is a popular word these days but quite often misused. And it's misused because it's hard to explain. I'll try my best.
Karma is not predestination, although the concept of "what goes around comes around" describes it well. The actions of past lives may affect future ones for the better or for the worse, but at the same time, free will always exists. For instance, Xena was trapped in a cycle of destruction but managed to turn her life around. Because of her efforts, in her future life, she was a revered peacekeeper. She grew more aware of her connection to the rest of the world as she strove to atone for her past actions; by doing this, she erased the negative karma that her years as a warlord built up.
Hinduism holds that all people go through different spiritual stages, and their karma varies accordingly. They may go through many stages in a lifetime or only one stage over several lifetimes. Taking the time to experience the stages as they come rather than trying to rush to the next is considered very important for spiritual growth. For instance, Xena is mistaken in wondering if she should give up fighting in order to reach her future saint-like status since her dharma in her present life involves being a warrior.
The idea is that eventually, when a person learns to live in harmony with the universe and transcend his or her ego, that person's karma will be resolved; the cycle of rebirth will end, and he or she will become one with God (a bit more about this on this page). That's what happened to Naima.
One analogy that seems to fit is that each life is something like a role in a play--certain things have been established and cannot be changed(the results of past actions), but the role may be played in drastically different ways by the actor, making it mean vastly different things. (I would argue that this is true whether past lives exist or not; even if I am theoretically free to will whatever I want, my identity and environmental factors make it very unlikely that I would, say, become a Skinhead.) A combination of free will and destiny.
Well, that was a very rushed explanation. Don't hesitate to send me questions if you're confused...
Xena: Warrior Princess is © MCA/Universal and whoever else legally owns it. This page is © 1999 shilpa.