What skillls, specifically, are needed to become a fashion designer?

Creativity, vision, gumption! An understanding of fabrics and how they will or will not flow, how they will lay when pieced together.

Sewing would be a good thing to know about!

Color theory (how different colors appear when placed next to other colors), including color psychology (how we "feel" about different colors...what emotions we feel when we see specific colors...which can also be subliminal).

I think too that some understanding of "the market" what the market will be willing to pay out for your styles would be a relative skill for a SUCCESSFUL designer to also possess. (Even if you hire someone to handle the marketing...the more you know about "the business" the more powerful you are and the better equipped you are to making intelligent INFORMED decisions!)

A lot of designers are very much in to the "Queen Rules" hype of designing. Now, I don't mean that they are all homosexuals, but that they sometimes think that everything THEY DO is so cutting edge perfect that they BELIEVE that if "you" don't like "it" its because YOU are too drab to "get it" or even to afford it. When in truth, "it" may not be even remotely practical, comfortable or "classic" enough to be of any true value for the masses.

An imagination and some art skills.... the best designers are those who do the unconventional (Westwood, Gautier etc...)

Redhawk basically answered the question, but I think you should Check out http://www.designerbloc.com/ it's a community for aspiring fashion designers to display their designs, get feedback, and meet other designers. It would help you if you wanted to get into fashion design

Creativity would be indispensible, a good sense of style, use of color and fabrics, I guess sewing skills and good knowledge of anatomy don't hurt either.