This freaked me out too. I was used to copying /Users/~/Library/Application Support/iCal from backup to system drive, but that didn't work. They're stored in /Users/~/Library/Calendars now.
What I did was:
1) open iCal
2) create calendars that matched my old ones
3) Import / Import an iCal file
4) navigate to your backup (likely positioned as detailed in the first path above) and click on the files held there
5) tell iCal which calendar to put your import into
6) repeat for all of them and then fix any muckups with matching the wrong source to destination calendars
7) run through everything in iCal until you're sure you're happy with it and then start backing up differently to reflect the new storage method
Hope that helps.