Newbie question

I have made a form and have used radiobuttons so people can choose a membership. example: <input type="radio" name="normalmember" value="normal member">normal member<br> <input type="radio" name="familymember" value="family member">Family member<br> <input type="radio" name="youthmember" value="youth member">youth member Now my question is if it is possible when they click on family member or youth member that beneeth that option comes 2 fields 1. name and 2. date of birth. I realy dont know how it can be done, so if some one can help on the may it will be much apreciated and i can learn more and experiment with it. Thanks in advance. Erwin