A family of Microsoft word processing software products for creating web, email, and print documents.
What design tab are you talking about?
The main tabs in Word 2010 are the same as Word 2007 except the Office Menu has been replace with a "File" tab in Office 2010 and there is no "Design" tab.
Are your referring to a contextual tab like TableTools>Design? It is in the same place.
Are you refering to the "Developer Tab?" FILE>OPTIONS>CUSTOMIZE RIBBON. In the MAIN TABS dialog check "Developer"