I recently learned from an issue that having the default created by MS which will allow for a user to create an entry with no end date could eventually lead to the entry itself being corrupt over time causing outlook entries to be out of synch by an hour. I suggest disabling this feature. For Outlook 2003 this will be similar. The registry entry will be Office10 vs Office12 as described below. Also, in the event you have some calendar entries that are off by an hour you can try running the MS TZ migration tool for Outlook. However, if the calendar entries are corrupt this tool will not help you. There is really no remedy to recover from a corrupt calendar event other than to delete and recreate it or move the event to the proper time manually.

1. Exit Outlook 2007.
2. Start Registry Editor.
* In Windows Vista, click Start
Collapse this imageExpand this image
the Start button
, type regedit in the Start Search box, and then press ENTER.

Collapse this imageExpand this image
User Account Control permission
If you are prompted for an administrator password or for confirmation, type the password, or provide confirmation.
* In Windows XP, click Start, click Run, type regedit in the Open box, and then click OK.
3. Locate and then click to select the following registry subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences
If you use policies, select the following registry subkey:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\Preferences
Note Both these registry keys perform the same function.
4. After you select the key that is specified in step 3, point to New on the Edit menu, and then click DWORD Value.
5. Type DisableRecurNoEnd, and then press ENTER.
6. Right-click DisableRecurNoEnd, and then click Modify.
7. In the Value data box, type 1, and then click OK.
8. On the File menu, click Exit to exit Registry Editor.

Resources: http://support.microsoft.com/kb/955449