Joseph,
What you COULD do andcwgat you SHOULD do are 2 different things. If you believe approaching your boss and negotiating a raise based on the salary of a coworker is a good idea then go for it. I would advise putting your negotiating skills to to work with an argument based on your accomplishments and value to the boss. Thats also the basis for nehotiating a salary for a new job. Not the salary of a coworker.