Oh for God's sake - if you want to sing just do it! But just don't expect to be a great singer straightaway - all you have to do is practice ... and practice, and practice, and practice, and ... well, you get the picture. Also record yourself (a cheapish digital voice recorder will do) and get some honest criticism from a workshop group - if you can find one in your area. It's all just a matter of hard (but often enjoyable) work and an ability to to take a certain amount of criticism (hopefully of the constructive variety).