Importing calendar data from Outlook to Lotus is not the most usual operation. On the Internet, there are rather plenty of examples and instructions describing how to make the exact opposite. The easiest operation is maybe this one.
In Outlook (2007 or 2010), go to your calendar view and perform a save as ... and select the ICS format. Use the date range option to limit the scope to future events only because later on during the import process, Lotus will impose a limit to maximum 500 events.
Once you have your ICS file, go to Lotus Notes (8.5 in my case) and open the Calendar. Select then file -> import and choose the ICS file type. Click OK and that's it.
Easier than expected.