I wish you luck. Most guys are immature buttwipes who simply don't have a clue how to take women seriously. Really, it isn't a question of you being a girl rider - it has a lot more with you simply being a girl.
That said, girls have done little to fix this problem. The majority of girls that are into bmx are into it FOR THE GUYS - not the riding. It's pretty easy to find a guy when there are 10,000 guys for every girl out there.
But, really, to be taken seriously, you gotta ride. Not sit on your behind looking pretty, but actually practicing. Go to the local park, or ride with the same people day in and day out. Make some friends, and try to find out if any road trips or jams or day trips are coming up and go to them. Ask and show an interest in the sport. If guys are showing a video of riding and you want to see it, then go see it.
for some girls out there and as far as I'm concerned Nena is one of the best female riders I have ever seen on a bike. An icepick on a 12 foot wall is just freakin' insane.