Thanks to the advice of other users here, I am now keeping my appointments on Google Calendar, which is synced to my Palm calendar. To search for those appointments I am using this app:
Google Calendar Search App:
This program searches (forward, backward or both directions) directly in your Google Calendars or Google Apps Calendars for the given search terms. Of course this program only makes sense, if one syncs his/her Palm Pre or Pixi calendar with Google Calendar.
Works like a champ.