What does Microsoft need beyond what Yahoo might have supplied: an expanded presence in online advertising and search with which to compete against Google?

Even as the buzz builds over a Microsoft move on AOL, (which would make sense if only to prevent Yahoo from acquiring the company), the feeling grows that the problems in Redmond, Wash., strike at the heart of the company's franchise.

Windows is under fire as never before.

Fifteen months after the introduction of Vista, 140 million computers have been sold with the operating system pre-installed. That impressive number, though, should be contrasted with what seems to be happening in large corporations.

Forrester Research noted that by the end of last year, only 6.3 percent of 50,000 corporate users surveyed were using Vista, with the market share of Windows XP hardly dented in the process (the defections came from users of the older Windows 2000).

The number of people who declare no interest in a Vista upgrade has forced Microsoft to reconsider its plans to stop selling Windows XP beyond June 30. XP is becoming the operating system that refuses to die, and it will live on in many small, mobile computers like the Asus Eee PC that can't hold up against the system demands of Vista. Dell will continue to sell and support XP after June 30, but only as a downgrade option that lets the company offer XP under a Vista license.

The less-than-overwhelming joy that has greeted Vista reflects dissatisfaction at the idea of buying new hardware just to run the latest operating system. We've gotten used to this model over the years as our programs grew in complexity and capability. Hardware was upgraded on a regular cycle to run them, but Vista may have pushed that model too far, springing it on a user community that seems to see little benefit in a demanding and expensive change.

With Microsoft making $15 billion a year on Windows, consumer and business software profits are key to future success. Thus when Gartner analysts recently described Windows as "collapsing" and the victim of an increasingly unadaptable code base, the alternatives before the company seemed stark. Is a smaller Windows possible, one that can compete in the area of specialized devices?

After all, Apple runs OS X on its iPhone, but Vista would swamp a hand-held device. And will Vista's successor, Windows 7, be able to compete against the expanding presence of Web applications?

Microsoft's challenges, meanwhile, play interestingly against what's happening at Yahoo, where independence may force a new corporate vision.

The Microsoft bidding war was all about figuring out what Yahoo is worth. However, there is no question that the company's list of innovative technologies is impressive. Its work in semantic search, which returns more targeted results than straight keyword searches, has potential in the competitive scrap against Google, and so does its Yahoo Pipes service, a way to string online resources together using intuitive, visual tools.

And then there's Flickr, Yahoo's photo-sharing acquisition, and the Del.icio.us bookmarking service.

The impression is of exciting technologies without clear direction in need of a strategy that moves beyond acquisition by a software giant such as Microsoft, whose corporate culture would doubtless have presented problems in Yahoo's search for continuing innovation. Yahoo doubtless is worth more than Microsoft offered if developed along the lines of semantic search and location-aware services.

The contrast with Apple could not be more stark.

Steve Jobs has used the iPod as a lever into growing PC sales, with the iPhone serving to build demand for Apple's operating system. Consumer-oriented Apple isn't making huge corporate inroads, but there's a growing buzz about the use of Macs in business that has spurred by remarkable sales numbers: a 51 percent sales increase in the March quarter over the previous year. Apple's new traction in the office is also a reflection of Microsoft's problems with Vista.

In other words, Apple, once a company with a bevy of interesting products and a lack of clear direction, has under Jobs managed to find its focus.

Macs, based on Intel, have made the transition for many users easy because the machines can run Windows whenever necessary. The beauty of the Mac: In a world where buyers are assailed by choices, Apple simplifies the work to six basic models. Today's market is beginning to reject complexity and bewildering options in favor of products that deliver and come in an understandable range.

Thus a snapshot of three major companies, with Apple on the most well-defined track.

Yahoo must sift through its assets to select the kind of company it wants to be, in hopes of parlaying some of its powerful technologies into new Web services as essential in their own way as iPods have become in the hardware line.

Microsoft's Windows woes are daunting, but the company has a long period in which to address them. Its installed base sees to that, a restless audience looking for reasons not to leave Windows behind.