Hi Geoff,
According to the following website
http://www2.fce.unsw.edu.au/nps/servlet/portalservice?GI_ID=System.LoggedOutInheritableArea&maxWnd=_Future_UG_InfoSysInfoTech
it's possible to major in Information Systems in either a BCom, BEco or BSc.
All of these programs are run by the Australian School of Business, so as far as O-Week is concerned it doesn't matter which you are enrolled in. You should attend the ASOB Faculty Welcome on the Tuesday of O-Week.
Having said that we usually advise people to go to multiple days of O-Week. On the day of your faculty welcome you'll be busy with talks from various academics in your faculty and school, faculty lunches, campus tours and other such stuff. If you can come in on another day as well you can get a chance to wander round the campus and check out all the non-academic stuff as well. Check out the O-Week website at
http://www.oweek.unsw.edu.au for a full run down of all that's on offer.
Hope that helps