I hear timing of sex and ovulation is more important than position. Look up a book called "Choose the sex of your baby: the natural way" it has a lot of information and for timing tips on both sexes. A lot of friends have succeeded with these methods and it's apparently easier for boys than girls!
I've also heard it has more to do with timing, rather than position. Closer to ovulation = better chance for a boy. I've also heard that gaining weight before conceiving can increase your chance for a boy.