EDIT: >_< Just realized this wasn't a question post *blush* how embarrassing. Helps to pay attention.
Removed my suggestions as everything I posted can already be found on the provided link.
Sorry for the confusing. Bookmarking provided link for future use
Looking at the buds of the plant you will find males have bigger buds than the females with 6 to 8 covering scales.
Female buds are smaller and more elongated and have only 2 covering scales.
If that doesn't work for ya a week before the leaves appear look at the plants flowers. Males have 4 to 6 tiny yellow flowers without petals and females have a single petalless flower which has a pistil, hypanthium, and two lobed perianth.
http://en.wikipedia.org/wiki/Hypanthium
http://en.wikipedia.org/wiki/Perianth
http://en.wikipedia.org/wiki/Gynoecium#Pistils