Can I map the iCal notes field to a calc in my database?
No. But you can map it to a field with an auto-enter calc that behaves like a calc.
Note that any phone numbers, email addresses, URLs, or physical addresses placed in this note field will be picked up as links when the event is viewed on your iPhone.
In the desktop version of iCal, these links don't show up as clickable, but if you right click on a URL in the notes field you'll see an option to "open url". URLs in notes also come through in Email notifications based on that event.