Saif is absolutely right. The gaming market has expanded exponentially in the past few years. Nearly half of the world's gaming population is women. I've met a ton of core gamer chicks in Oklahoma. Lots of Smash girls and lots of Halo/CoD clans are around if you look for them, or talk to people. You'll also find that most anime girls tend to double as J-RPG fans.
If you're looking to convert a girl to gaming, you've got to start small. Don't throw Gears of War at her and expect a reaction. If anything, you've got to give Nintendo a lot of credit for helping make gaming socially acceptable for women. Use that. The Wii is your friend and a powerful tool. And even if that demographic skews on the casual, more of them than you would think actually wind up advancing into more traditional core games. Go with something simple like Dr. Mario. I've learned through experience that Dr. Mario is literally crack for female gamers. I've never met a girl who didn't instantly fall in love with at least that single game, and then wound up wanting to play more competitive puzzle titles. If you're wanting to convince a girl to play a fighting game with you, go with Soul Calibur IV (and soon SCV). The "character creation/dress up fighting doll" aspect is a HUGE draw. I know at least 15 girls off the top of my head who love Soul Calibur.
If you're smart, and pick your games intelligently, you can get just about any girl to fall in love with gaming. She may not particularly fall in love with the games you play, but at least she'll understand fully why you love them.