Since Outlook 2000/2002 doesn't work well on Vista, it's worth trying the calendar application that is included with Vista if you aren't interested in upgrading to Outlook 2007 and only use Outlook because you need a calendar. The only problem is getting your appointments into Calendar. Vista Calendar imports *.ics format but Outlook 2003 and earlier can't export to a single file *ics. Outlook 2007 can export all of your appointments to one ics file, assuming you have access to a copy.
If you use Gmail, you can Export your calendar from Outlook as a CSV formatted file and import it into Gmail, then export it as an iCal which you can import into Windows Calendar.
Outlook supports exporting single items in iCal format. It also supports forwarding selected calendar events as iCals. You can switch to a table view (By categories view works well) Select the items you need in Windows Calendar and use Actions, Forward as iCal. Send the message to an account you'll access in Vista. Because you need to import each appointment individually, this method works best for a very limited number of appointments. It does not work well with recurring appointments.
Utilities you can try:
Outlook to iCal Export Utility for Windows (VB Macro)
outlook2ical.js - adapted from Outlook to iCal Export Utility