I'm not a horse owner, I'm only 13, but I wouldn't see trimming your horse's feet on your own a good idea. By 'your own' I mean by reading a book and trying it yourself. (Sorry if this sounds like I am directing this at you, I am not). I think what you mean is that you can get one of those barefoot rasps, which I think are ok. You can just round out the edges till a farrier comes for a trim, but they shouldn't be used to trim your horse's fit, just round the edges to get rid of a few chips.
My BO went to farrier school after not being able to find a decent farrier in the area. He leaves his horses barefoot and they are happy and healthy. He actually trimmed one today.
I think if someone wanted to trim their horses' feet, a good option would be to get some instruction from a farrier and see if he can teach you how to trim properly, and supervise you. It is so easy to ruin a horse's feet or make them sore with a wrong move or too short of a trim or a trim at the wrong angle. Although it is possible to learn, I think it would be a better option to just stick with a trusted professional. Lot less chance for error :)