You can download a trial of Adobe Illustrator, which is basically the industry standard for all Vector work. It'll last you a good thirty days. I recommend using the "Vectorscribe" plug in which you can also use on a trial basis. They have an excellent series of tutorials to teach you how to work the program.

Some people like using Photoshop for their vectoring, but this is a much more difficult way to do it and your results will not be as good.

I believe there are some freeware vector programs out there, but I'm not familiar with them and Illustrator will have enough documentation around that you can figure it out in a week or two of playing with it.

If you want more than a trial and a free, open source program, then go with Inkscape.