You can't conceive before ovulation! You might make love before ovulation and conceive when you ovulate, though, because sperm can live in the reproductive tract for up to 72 hours.
I read somewhere that Y-chromosomes (for boys) move
faster but don't last as long as X-chromosomes (for girls),so have sex as close as possible to ovulation if a boy is what you want. If you try to conceive two to four days before you ovulate, you'll most likely have a girl.
There are a few schools of thought on that though...and it remains to be seen...we conceived by making love on ovulation day and then two days later, it being a busy weekend (we had guests *naughty giggle*)
Sue