Using the Microsoft.TeamFoundation.WorkItemTracking.Controls assembly it is possibe to display WorkItems. Here is a little demo application that will display all the WorkItems that have been changed by one of the given users in the given range

Feel free to download the source: WorkItemTracker.zip

Edit (05/03/2008):

Refactored the code a little and added some features like sortable columns, loading default tfsserver and users from App.Config, …