Theres a stupid change to SQL Management Studio in 2008. When you go into design view in a table and make a change to a table structure that requires the table to be recreated (such as changing Allow Nulls, or making a column an Identity), the damn thing won't allow you to save the changes. Instead you'll get an irritating message allowing you only a Cancel option - so you lose your changes and are stuck.
After a lot of RDC to the server to use its 2005 Management Studio, I found this solution:
Go to: Tools > Options > Designers > Tables and Designers
and uncheck the Prevent Saving Changes that require table re-creation option
This will give you "normal" functionality whereby you can amend a table all you like.