Choosing the gender of my child

I keep on reading that having sex before ovulation will increase the chance of having a baby girl.

I also read that if I want to have a boy then we should be making love after ovulation.

I want to know if this stuff is a true fact or just another urban myth, or an old wifes tale about conceiving a boy?

We really want a girl baby and we are trying to conceive at the moment, so far we have just been doing it as often as we can. Since we want to have a girl, if this method is true we should be doing it less often but know when to do it.

How can I know that I am about to ovulate? Can I get some sort of test from the dr or buy a ovulation predictor home kit somewhere?