Jessica -
Charity events can be anything from dance marathons, to volunteering at homeless shelters to selling flowers on campus for Valentines Day. Each sorority has it's own 'pet' project, in addition, they often help out in the philanthropy projects of other GLOs.
As far as parties go, all NPC housing is alcohol free, so the parties that might be held at a sorority house or lodge would have to conform to those rules. You'll see when you go through recruitment that sorority houses are usually quite nice, upscale even, in their amenities and decor. The chapter certainly wouldn't want this home-like environment damaged by a loud pre-game party.
Check out my recruitment page for some informaton on NPC Rush. In SoCal you will also find many Latino, Asian and multi-cultural GLOs. Research the groups on your chosen campus carefully and rush where you feel the most comfortable. The nice thing about the NPC and NPHC groups is that you can usually find members world-wide, meaning that even back home in the UK, you might be able to get involved in either an alumnae chapter for your sorority OR a Panhellenic Association for alumnae (representing alumnae from different NPC sororities).
Best of luck!
Barbara
Zeta Tau Alpha, alumna
http://tallahasseezta.tripod.com http://panhellenic.tripod.com/FAQ.html