If I decide to migrate my legacy Palm/Outlook calendar data to iCal, this is a handy reference: macosxhints.com - Import .csv and other text files to iCal. The comments suggest other options.
For now I simply ended my Outlook calendar and started using the iPhone calendar. That was the least trouble for the moment.
[Update 8/16/08: Much later I realized I could have used Missing Sync for Palm OS to sync my Palm to iCal. I have a license from eons ago, when we used to sync my wife's SONY PalmOS device to the iMac. I may still do that to get legacy data into the calendar, but really I'm better off archiving that data.
Update 10/2/2009: Another method.