I believe that the spiritual part of a person has many pieces -- soul, spirit, fetch -- whatever you want to call them. I think they're all integral parts of human existance. I believe that we have dreaming spirits, the soul that deals with rational mind and daylight reality, soul parts that walk outside our body dealing with soul business while our bodies deal with more mundane things. I believe that there are souls and spirits that gather around us according to our perceptions and abilities, helping us and guiding us through difficult situations. Some might call these "guardian angels" while others might refer to them as "spirit guides" or "totems" or by other names.
In shamanic belief (it's one of the types of belief I ascribe to), one can lose parts of one's soul through shock or trauma, by violating certain kinds of geasa or taboos, or by being attacked by non-corporeal entities or other humans on a spiritual level.
A psychologist named Bill Plotkin wrote a lovely book called Soulcraft: Crossing into the Mysteries of Nature and Psyche that I think expresses his view of the difference between soul and spirit very nicely. It's a well written, very useful book, and for those with an inclination to nature reverence or mysticism of any sort, I'd highly recommend reading it through and considering trying some of the exercises he suggests.
He says:
"By soul I mean the vital, mysterious, and wild core of our individual selves, an essence unique to each person, qualities found in layers of the self much deeper than our personalities. By spirit I mean the single, great, and eternal mystery that permeates and animates everything in the universe and yet transcends all. Ultimately, each soul exists as an agent for spirit."
This said, I believe in many kinds of spirits -- ancestor spirits, animal spirits, tree spirits, stone spirits, river and mountain and cloud spirits. My belief is fairly animist at root. It is my belief that everything natural that exists, and some things created by humans, are animated by spirit -- that everything has spirit, is spirit. I believe, in essence that all things in nature have a soul of some sort. I don't believe that any of it is inherently evil, though I do believe that the desires and goals of much of the universe are not those of humans, and that when we and these other spirits act at cross-purposes, humans may perceive a lot of it as "evil" because it runs counter to our own natures and our potential for survival. But if a bear attacks and kills a human, it's not "evil". Most of the time it's because a human is disturbing bear territory, is too close to cubs, or has somehow otherwise provoked the bear.
Most forms of Paganism don't accept the existence of "Satan" -- a specific deity devoted to evildoing. To me, saying that non-human/angelic spirits are "satanic" seems quite absurd. In a polytheist reality like mine, the idea that there is one great maker of Evil makes no sense, as there is no one great maker of Good. Within the realm of my own belief, derived from early Irish and Scottish forms of Paganism, there was no one original creation, for instance. The creation of different places and features of landscape occurred at different times and were caused by different spirits or deities, in the same way that the Adirondaks of the east coast of the US are far more ancient mountains than the Himalayas. To me, creation is an ongoing process, not a static, one-time event that requires one Great Maker.
I know this is straying somewhat from the topic, but I did want to address that point, as it was brought up in another post.
A note to Aerylon -- a lot of people convert from Christianity to Wicca or other forms of Paganism. I did it myself. In fact, the majority of modern Pagans in the west are converts from Christianity and Judaeism. I was raised in a fairly fundamentalist family, though my own parents are more or less Christian agnostic and a lapsed Catholic atheist. I was taken to church every Sunday "because it's good for you." I went to a fundamentalist Christian private school in 5th and 6th grades. What all that exposure taught me was that Christianity as it was presented in these environments made no sense to me. What I read of Paganism, however, did make sense. It took a while to let go of all the Christian programming, and I will admit that a certain amount still lurks under the surface, but for the most part the kind of Christianity I was raised in is very alien to me now. I had a hard time justifying those beliefs when I had them, and now they feel like they come from some different planet. Blessings to those for whom Christianity expresses a soul-truth, but religion, like socks, is not one size fits all. Or, as Robert Heinlein might have put it, being in the wrong religion for your heart is like socks on a rooster -- it looks funny and annoys the rooster.
but that's ok 
