The scoop here is that for various reasons, (i.e., database integrity, data and relationship reasons I assume) you can't delete work items from Team Foundation Server (not as you and I would think about deletion of work items). Essentially, you place them into a state where you can't easily "see" them again so that when uers run Team Foundation Server queries, they no longer show up. The way to accomplish this is to do the following:
First Resolve the item. Depending on the item, set its state to "Resolved" or "Closed". Then set its reason field to "Obsolete". These actions make the work item invisible to most all queries and serve to logically delete the work item.
If you were like me, you had a ton of work items you were playing around with and the thought of going through each one to set its status was daunting. You could cheat and head right to the DB to update the items, but that is dangerous. What I did was to open the All Work Items query in Excel and then use a "fill down" method to quickly set state and resolution reason on each of the items (I had 200 to get rid of). Then I published the items and they were removed.