My daughter is 5 and she is definitely a "tomboy". She always wants to wear Spiderman, and other superhero clothes, even her cousin's old "boy" underware. When we go over to his house, she is obsessed with wearing all his clothes. She always wants Spiderman birthday parties as well. However, she also loves Hannah Montana. All her friends are boys, can't even think of one girl. These things don't worry me b/c I was a major tomboy. I would never wear dresses or skirts at all! What does bother me is that she says she wants to be a boy. Bother, yes, in a sense that I want to raise her with support. But I need to know how to handle this. Do I just "let it roll" and worry about it when she's older or start thinking that she might have gender issues. I just don't want to shame her into believing that she should be happy that she's a girl. I want to know how to support her best. The posts by others has really helped and will help more when I can spend more time reading them all.
As a social worker, working with parents and kids on a regular basis, I have neither seen nor read any research that would indicate that your daughter has a problem. Kids experiment with identity all throughout the life cycle.
The best support you can give your child is to let her play out her interests, let her be herself and yes, do not under any circumstances shame her. You have the benefit of your own experience to know that tomboys can grow up to be well-adjusted women. Whose to say that her interest in boy things isn't paving the way for an adult who is well rounded and empathetic to both genders.
I encourage you not to worry. If when she grows up she does have "gender issues," these can all be dealt with. At this point, she sounds like a normal five year old little girl.