Get your recs sent to the chapters before school starts in the fall, or soon there-after. The houses work on recruitment all fall, so if your information is there, it will be seen, if it's not, you may get lost in the shuffle come spring.
A rush packet is the information and photos sent to the chapters through your recommender (so you need to send all this to whoever is writing your main rec). It is comprised of the recommedation form, photos, resume, letters of support, and transcript (if the sorority wants it - mine doesn't, but some do).
I rushed at SMU back in "the day"

, but things haven't changed that much according to my sources!