Well, the first time you sync your iPhone to your Mac, you will be given the opportunity to sync back the PIM data (calendar, contacts, bookmarks) and either merge it with any information currently in the Mac applications (ie, iCal & Address Book), or replace anything in those applications.
If you haven't actually setup any data in iCal or Address Book on your new Mac, you can select "Replace Info" safely enough and the information from your iPhone's calendar and address book will be transferred to your Mac.
Other content such as music and videos will be removed and replaced with the corresponding content from the iTunes library on your new Mac, so you'll want to either transfer your iTunes library from your PC separately, or look to a tool that can recovery this information from your iPhone (
www.findleydesigns.com has one of the few applications for this I'm aware of that is iPhone compatible, although if you also have a traditional iPod model there are numerous other software applications for this as well).
See our
August 2, 2007 Ask iLounge Column for more information on syncing an iPhone to a new/different computer.