VB.NET classes to find /update Exchange Outlook appointments

Hi, We have a requirement for some VB.net classes that will search and update appointments in multiple calendars in an Exchange Server public folder. The search class will be passed a string value (up to 20 characters) and will need to search calendar appointments by a single user-defined field. The class will then return the appointment so that it can be updated and saved. There will be up to 30 calendars in the public folder but we will not know which calendar the appointment belongs so the code needs run quickly - it will be too slow to iterate through each appointment in each calendar. The solution will have to include a maintenance feature which will allow the administrator to select the public folder that the search and update components will use. This maintenance feature will probably only be used once when the software is installed. In your bid, please include a brief description of what search and update methods you would use. It will use Exchange Server 2007. It will need to be written in VB.net and use .net framework 3.5 and we will require all of the source code. Thank you