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.

In his keynote speech at the 2008 International Consumer Electronics Show (CES), Bill Gates talked about what he called the commercial success of Windows Vista. “I’m pleased to say that we’ve got over 100 million people using Vista now, and that’s a very significant milestone,” he said.

Many commentators regard that figure as disappointing, however. One forecast speculated that 270m units would be sold during 2007. Microsoft’s numbers may lag the market, since the vitally important Christmas selling season is barely over. Microsoft officials have pointed out that it’s difficult to know how many units of Vista are in use in large corporations since the licenses they buy allow them to deploy either Vista or XP.

In addition, the shipping of Vista’s Service Pack 1 (SP1) later this quarter should shake the market into action.

Richard Shim, research manager at analysis firm IDC, said, “Vista has received a lukewarm response because Microsoft hasn’t made a good case for upgrading”.

Another commented, “Office 2007 only takes marginal advantage of Vista. The impact of Vista is still alive,” he added. “It’s not as influential as it was, but I wouldn’t call it a failure”.

Robert X. Cringely, the veteran technology writer over at PBS, recently forecast that “Microsoft will indefinitely extend the life of Windows XP, acknowledging the failure of Windows Vista, which will require another generation of hardware (and another $5 billion in R and D) to finally look good three years from now.”