This is kinda funny. Somebody asked on Yahoo Answers:
If you suck at singing and you practice will you get better?
And the best answer, as voted on by the Yahoo Answers users i guess:
Depends. Sometimes people can make their voices amazing by just singing along with other singers. Other times you need to get a teacher. I personally recomend getting a teacher. I would also find a teacher who focuses more on itailian and theatrical stuff because that music really helps. It might sound lame but its the basics. That way if you are singing pop, rock, or whatever you can apply basics and then make it your own. Also you wont hurt your voice.