This topic is one I think about a lot. As a few people have mentioned, I'm not sure the goal should be to get more "women" into gaming. That's way too broad of a category and there's so much difference between women that it's near impossible to come up with a strategy. Even if we can make broad generalizations about women (and that's pretty controversial), it's pretty unlikely that those generalizations will help us with an individual woman.
If we concentrate on women who enjoy fantasy, especially those who enjoy computer and video game fantasy RPGs, it becomes a bit easier.
One thing that might help is to recognize as valid other ways of playing the game. This would help not only get more women to play, but more men as well. Not everyone enjoys playing the same way and even within the traditional view of how to play D&D, there's a wide variance.
Shifting emphasis to overcoming challenges and away from overcoming challenges by killing creatures might help. I don't think this will water down the game to a point where men wouldn't enjoy it anymore as Burning Wheel and The One Ring both do this and what I hear from the OSR community is that they like this way of playing as well. Schwalb's
Reexamining the Dungeon also discussed this a bit by tying XP to accomplishing an objective rather than to killing monsters.
Also recognizing the mastery comes in multiple forms. Not everyone, regardless of gender, cares about character optimization but a fair number of online communities seem to emphasize it and assume that all players will "evolve" to the point of seeking that type of system mastery. This can reinforce personal opinions about who plays and why without necessarily reflecting the broader audience.
While the people at the table have a profound effect on whether or not an individual woman decides to play, there are things that game companies could do. Paizo and WotC both have worked on getting a greater diversity of female characters in the artwork. But one area where I see room for improvement is in the gear available for characters. Most of the gear is still masculine or unisex. What's awesome is that gear doesn't require a lot of system knowledge. Articles or even books on gear would be a great entry point for women who are new to the game or maybe new to design to add to the game without taking away anything from other parts of the game.
Actually, in general, encouraging the women who currently are playing to share their experiences and produce fan and professional content for the game would help tremendously.
Sorry, I got a bit carried away with this. I hope you all don't mind too much.