Unfortunately the iCal/iCalendar/etc. terms are very overloaded and confusing. The latest standards document these are all based off of (RFC 2445) calls itself iCalendar, so that's the term I use. I think Apple's iCal program and Google's export to .ics are all using some variant of the iCalendar standard. All this is just the roundabout way of saying that you should try importing your Google Calendar file directly into calend via the "Import iCal" menu item and see what happens.