I don\'t see any obvious way to import ICS files into Google Calendar from the API docs here:
http://code.google.com/apis/calendar/developers_guide_protocol.html
For my iCal2GCal app I'm using the Googlecalendar Ruby Gem to both parse .ics files and then add the events inside to a Googlecalendar. It might give you some ideas on how to go about it. You can check out the full source code.