My ISP reconfigured its email stuff and I've had to redo a bunch of stuff on my BB.
Anyway, when I re-synced my BB with Outlook, in the Week calendar view all the birthday entries suddenly turned into entries that take up a whole day worth of space rather than just appearing at the top as a small entry without a particular time attached.
If you're still having the problem, make sure the time zones on both are the same. Mine took all day entries in Outlook and posted them as 23:00 on the previous day to 23:00 on the event day, because the phone was in a different time zone.