'Where ... does the system store a users iCal and Address book info?' - it (the 'System' ... 'MacOS X') does not store any information of either application - anywhwere. Each application - 'Address Book' and 'iCal' stores its own generated files.
'Address Book' creates and maintains the file of 'com.apple.AddressBook.plist'; and also, the folder (of items) '~/Library/Application\ Support/AddressBook'.
There are also the '/Library/Address\ Book\ Plug-Ins' and '~/Library/Address\ Book\ Plug-Ins' folders, whose items add functionality to 'Address Book'; and finally, the '~/Library/Caches/Address\ Book' folder (of items).
'iCal' creates and maintains the files of '~/Library/Preferences/com.apple.iCal.plist' and '~/Library/Preferences/com.apple.iCal.AlarmScheduler.plist'; and also, the folder (of items) '~/Library/Application\ Support/iCal'.