http://www.macosxhints.com/article.php?story=20060821073102694

I modified it to run from the menu. It works great and is free.

Select the View>Message>Previous Alternative menu command in Mail - the text turns into an attachment named “meeting.ics” (your mileage may vary. Double-click on the attachment and away it goes into iCal. Even easier is to use the keyboard shortcut - Command-[

There are, from time to time issues where the time zone for the meeting is munged because either iCal doesn’t parse the Outlook/Exchange formatted .ics file correctly, or the data in the file is mal-formed. Garbage in, garbage out.

I think Mail might do a better job of dealing with Outlook-spawned .ics files. There is no way to know, just looking at the mail, that it bears an iCal-compatible payload. It certainly doesn’t show up in the iCal Notifications pane as iCal-generated .ics attachments do.

Well, hopefully he can address this, as this looks like an otherwise very useful utility for those of us who are saddled with having to co-exist with Exchange users.

Unfortunately, it doesn’t appear at this point that it will handle invitations that are downloaded directly from an Exchange server (ie, via Mail as an IMAP client), since these tend to use embedded HTTP URLs back to the Outlook Web Access server rather than attached ICS/VCS files.