Americans may have seen the new Microsoft TV ad in which Bill Gates and Jerry Seinfeld strut their stuff in aid of the ailing Windows Vista brand.

The ad started airing in the U.S. last week and is the first in a $300 million campaign to reinvigorate Windows, long considered one of the strongest brands in technology.

The expensive advertising highlights a number of concerns:

* Widespread lack of enthusiasm for Windows Vista, especially among corporate IT groups, which regard it as a step backwards from XP. They hope to hang on without upgrading until Microsoft’s next-generation operating system arrives.

* Apple’s constant attacks on Windows via its witty and successful PC versus Mac marketing campaign.

* Microsoft’s inept confusion of the Windows brand with its Windows Live attempt at web services, from security and anti-virus to email and IM.

The real challenge, of course, is to generate excitement about a box of software that most users take for granted, and to develop more distinct, compelling messages around what Windows offers to consumers, enterprises and software developers.

Otherwise, Vista could be the new Windows ME.