Read this thread:
http://www.greekchat.com/gcforums/sh...ad.php?t=93174
1. There is not entity that you have to "register" your group with, unless you plan on affiliating with a campus (which doesn't seem to be the case).
2. You might be able to attend, but I don't know of any campuses that will allow non-recognized groups to participate in university events (liability/insurance reasons). If you don't want to be affiliated with a school, I don't see why you'd want to participate in these things anyway.
...and this is going to be asked eventually, but I might as well bring it up now: There are several organizations that are already in existence. Why are you starting a new one? What will make your group stand out from the others?