Outlook 2007 – with the lasted update installed – now supports multi-year recurrences. This means you won’t need to use 24 months to create appointments which recur every 2 years. Sorry, that is the only change to recurrence patterns. Maybe next time we’ll see quarterly appointments. I don’t think we’ll ever see fifth week in a month because making Outlook handle it correctly when there is not a 5th week in a month would be too difficult.

See
An update is available for Outlook 2007 that improves Internet Calendar functionality and improves compatibility with IMAP servers (KB 950219)