iCal syncing is a feature of Delicious Library and it should happen automatically. In Mac OS X 10.4 "Tiger" or higher, Delicious Library needs approval to sync with your iCal calendar and will present an "Allow" dialog early during initial use.

If you disallowed this original sync, Delicious Library will be blocked from future syncing with iCal. To re-instantiate the sync process, you must reset your sync history.

This can be done from the iSync application in your Applications folder. Open iSync and, from the iSync menu choose Preferences. Pressing "Reset Sync History" will reset the system's sync settings.

The next time you launch Delicious Library and make a change after resetting the sync history, you will be prompted again if you would like to allow Delicious Library to sync its calendars.