There are a set of stored procedures that get created when you use various visual tools against SQL Server. For example, this can happen using Visual Studio's Server Explorer to view/create database objects, or something as simple as opening the diagrams node in Enterprise Manager. Even if you haven't created any diagrams, the procedures get created.
These stored procedures are used mainly for source code generation, and the dt_ prefix stands for "DaVinci Tools"—an early codename for this technology (but it wasn't fully implemented, and is no longer present in SQL Server 2005).
These objects are more of a nuisance than anything, especially in databases with a small number of procedures (and when half of them start with A-C and the rest are E+).
They are safe to delete, provided you are not using full-blooded source control and Visual Studio integration, and you do not have any diagrams that you want to keep around. However, you might be having problems deleting these stored procedures from Enterprise Manager:

Enterprise Manager marks these procedures as system objects, so does not allow you to delete them. Thankfully, Query Analyzer is not so restrictive. Run the following script, which will give you an output of a series of DROP statements.
SET NOCOUNT ON SELECT 'DROP PROC '+ROUTINE_SCHEMA+'.'+ROUTINE_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_NAME LIKE 'dt[_]%' AND OBJECTPROPERTY(OBJECT_ID ( ROUTINE_SCHEMA+'.'+ROUTINE_NAME ), 'IsMsShipped') = 1 |
Copy the output from the lower pane to the top pane, hit F5, and voila! No more stupid dt_ objects. Until the next time you connect to the database using Visual Studio, or you accidentally click on the diagrams pane.
As an aside, the SET NOCOUNT ON statement is used in this case so that you can use select all (CTRL+A) in the bottom pane, and not have to manually remove the "31 row(s) affected" message before running the code—otherwise you get an error message similar to the following:
Server: Msg 170, Level 15, State 1, Line 34 Line 1: Incorrect syntax near '31'. |