Inkscape's Trace Bitmap, in the Path menu, could do what you want as far as tracing an outline. However I find that unless the image is quite simple, it's not an acceptable solution. I recently found an online tracer here :
http://www.roitsystems.com/cgi-bin/autotrace/tracer.pl It seems to do the trace differently, but not really better, imo.
The 2nd part of your question cannot be easily answered. As with anything else, it's practice, practice, practice....which goes a little faster if you have some inherent artistic ability. But either way, one must invest some time and energy to be successful. I would suggest following some tutorials, and you can find a couple of links in my signature. There are also some in the Inkscape manual, found in the Help menu. Are you interested in doing cartoon type of work, or posters, or photo-realistic, or even abstract art? There are different skill sets needed for each, and it truly is only a matter of choosing what you want to do.
You might want to browse the "Show It Off" group of forums, to see what kind of work is being done with Inkscape. I've just started on what will be my most ambitious work with Inkscape, although I hesitate to call myself an artist. I'm attempting to reproduce a photo. It's posted in the Work in Progress forum, and I intend to post screen shots as I work -- partly in hopes of getting some constructive criticisim, and partly to show folks like you a generalized Inkscape process. I know it has helped me a lot to learn how other people use Inkscape, so just trying to, you know, give something back

But by far, my best advice would be to find a tutorial, and jump right in
