Export your calendar events from Outlook as a tab-delimited text file, open the text file in Excel (or other spreadsheet which can read delimited text files), change the appropriate column headings to read: Title, Date (Start), Start Time, End Date, End Time, Category 1, Category 2, and Private. Delete any remaining columns. Save in the same delimited text format as the file was when you opened it.
Now download and install the newest free Palm Desktop for OS X, import this freshly edited delimited text file into the Palm Desktop datebook, then turn around and export the datebook from Palm Desktop as a vCal file, which imports just fine into iCal. Also, Entourage says it will import from Palm Desktop, though I've not tried that.
Phew! That was easy wasn't it?

