Well, first of all, you need a decent graphics program. Photoshop is probably best, but unless you feel like forking over $600, get the trial. PSP is also good, I hear (I wouldn't know; I use a Mac).
Second, you can't get anywhere without learning how to use the program. I learned how to use PS by reading lots and lots of tutorials. A simple google search on '[put name of your graphics program here] tutorials' will result in many, many links.
And lastly- when you're familiar with the program, practise, practise, practise! You can't expect to make a masterpiece on your first try. =)
Hope this helps!
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