I have herd of a way to help predict a girl, but not climaxing is definitly not it. I think someone is definitly pulling your leg on that one!
Now, I have herd of this on parenting shows and on some sites, but of course is not 100% sure going to give you a girl. It will only help your odds.
Basically male sperm (Y sperm) swims faster than a female sperm (x sperm). However, the female sperm live longer.
So if you have sex the day before or the day of ovulation the male sperm will get there faster. But, if you have sex a few days before ovulation the male sperm will have died by the time ovulation occurs, leaving the female sperm.
In order to do this you would have to know and understand your cycle very well. You would have to know exactly when you will ovulate to know to have sex a few days before. If you are considering this method I suggest reading the book Taking Charge Of Your Fertility to help you determine when your ovuation occurs. (Its not always on day 14 like most people think) Or you can check out the web site
Taking Charge of Your Fertility
Of couse, like I said, this isn't going to
make sure you have a girl, it will only greaten your odds.
Baby planning time - Gender selection is an example of a site with this method, of course you can find many others by simply searching it.