I've gotta go with Xinoxlx on this, the topic may not have been rude to start with but it was pretty bait-like - as if designed to attract the kind of responses he seems to revel in. Given his proclivities for hate-mongering and homophobia in the joke thread I don't think the OP needs defending.
Also, Azrailx may have been crude in this thread, but not inacurate. The joke thread is also rather funny.
Regardless, I shall attempt to address the original topic:
Games with highly male player-bases can be uncomfortable to women, not least because most men believe they should be treated differently, without being entirely clear on how they should be treated differently; it often outs itself in fairly random gifts or other acts which may be kind, but deffinately seem creepy to the woman.
When I played WoW for a couple of months (ugh) I was in a guild with friends from Homeworld 2, which included some female gamers. They were competetive and so fit in well with a successful raiding guild. It was also the only place I ever saw a successful online-couple being formed, while still in highschool; they eventually went on to go to the same uni but I don't know what happened after that. My wife on the other hand, when she tried WoW out, wasn't competitive at all and joined a group of role-players; this didn't work out very well, all the "milady"s and bouquets of pixels were odd enough, but the reaction to her saying she was married didn't just return things to a semi-normal state but made people positively hostile.
Different games have different populations, and women tend to integrate into traditionally male-dominated comunities (such as RTS ones, or the harsher MMOs) in different ways.
EVE, my MMO of prefference for instance has a 97% male population according to the votes for the player-representatives-council from last year or the year before, it simply doesn't seem to be an attractive concept for women.Those who do play tend to either out-male the men, being 'one of the guys' to let people forget they're female (the leader of one of the former major alliances, Foyle, could very easily have auditioned for the QoT personality-wise. Mother of 2 and pure eveil in-game, not feminine at all.), or they find other women to hang out with. There's a few all-female corps and others run by women.
All of that is only an issue though if people know that they're female (voice coms for instance). If people don't know, it's much easier for them to do whatever they want without getting hassled. That includes pwning you.
Yes, there will be girls playing. No, they probably don't want to be very open about their gender just yet, and there's no reason they should be; it shouldn't change how you treat them, but it will. If they're nubs, help them as you would a male nub... or shout at them in caps like you would at a male nub. If they beat you... it raelly isn't a magical new experience. 90% chance you've already been beaten by a female gamer without you knowing it, how would knowing it change the experience?