I think the idea Ballmer's referring to is the API that salesforce.com has built...

gibsonf1 on July 11, 2007 | parent | context | favorite | on: Ballmer hints at Microsoft's future in the 'cloud'

I think the idea Ballmer's referring to is the API that salesforce.com has built to let developers use their systems to provide apps. MS wants to get a piece (or should I say the whole pie) of that business.