About the dorms, I know that Edinboro University had Male and Female dormatories and 1 Co-ed dormatory, that's it. So, perhaps one dorm would be Co-ed, and the rest would be single gender.
Err... I think What Tim's trying to say was Edinboro University (where I went) had co-ed dorms. We USED to have an all girls dorm, but that changed. Now all they have are all girls and all guys FLOORS. You can also choose to live on a mixed girl+guy floor. Though I am certain that you will be given a same gender roommate ^_~As far as wether or not Shinonome High had co-ed dorms, or even more than ONE dorm, I don't know and I'm not sure if it's made clear in the OVA.