Gina Lynn,
[*]The resources are certainly out there for those who are interested in GLOS:
www.npcwomen.org and
www.nicindy.org are links to the governing bodies for sororities and fraternities, respectively. In addition, most schools have a Panhellenic or Greek Council website, in addition to individual chapters. Even if someone does not have access to the internet, there are ways to research your organization. I know during my senior year in high school, the teachers who were members of NPC sororities, along with the president of local Panhellenic, came to talk with the senior girls about Rush (of course, this was in Florida, with two of the nation's largest Greek systems, so this probably doesn't happen everywhere). In many colleges and universities, the Panhellenic or Greek Council will send freshmen information regarding Rush over the summer.
[*]In regards to your first question, yes...some schools hold Rush in the first two or three weeks of the semester, and in some cases, before school even starts (I have friends who moved into their dorms two weeks prior to the start of their freshman year in order to be there for Rush). Not all schools, however, do this. The purpose of an early Rush is to get the girls in a house they like before they're in school too long, before certain reputations (i.e., "they're all snobs/sluts/nerds") can taint a girl's opinion of a group. It is, in this case, up to the girl to learn basics about the sororities on campus (especially if she's a legacy--although, supposedly, it does nothing to influence the sorority's decision) before she gets on campus, either from the Internet, local Panhellenic, or from friends who attend that school.
[*]Your second question...the way Rush works, a girl often doesn't get an invite back from a group she has had her eyes set on. I know we were constantly told (this is before I started college, my college has a very informal Rush) to concentrate on the houses that have invited you back, and you will be sure to find a house with which you are happy, and in which you feel as if you could find a home. Usually, if a girl doesn't want to be a member of a certain sorority at all, she won't pledge.