Setting the IDENTITY flag of an existing column in SQL Server 2000 September, 2006
Apparently you cannot set the IDENTITY flag for a column by simply using an ALTER TABLE/ALTER COLUMN in SQL Server 2000 (Not sure about 2005). I spent some time roaming around BOL and couldn't seem to figure out how to do it. From what I have been reading Enterprise Manager has to jump through some hoops to accomplish this when you set the flag though the GUI.