Google is way out in front, with hints of tiring. Yahoo! is a distant second, but gaining. Microsoft is the only other runner on the track — several lengths behind, no less — but the aging champion won't quit.

Microsoft appears poised for a major sprint this year as it beefs up online or "live" versions of its software through new services called Windows Live and Office Live.

Other Web Thoroughbreds are still running their hearts out, but they're so far back in the premium-stakes race that you might as well put them on a different track.

Most interesting is how the potential champions are moving onto new turf at breakneck speed, obvious by the feverish pace of their buying over the past year.

Popular takeover targets included providers of Internet phone service, mobile data and digital advertising technology. It doesn't take much imagination to look at what those Internet stallions are buying and see them girding for runs against traditional phone companies, wireless carriers and established media giants.

Just last month, Google said it would pony up potentially more than $1 billion for local radio-advertising firm dMarc Broadcasting and an undisclosed amount for Reqwireless, a wireless software firm.

Yahoo! announced last month it had bought itsy-bitsy startup WebJay, which lets people share music playlists. In December, it gobbled up the online bookmark-sharing service del.icio.us. And Yahoo! bought several other content-sharing Web services last year, including Upcoming.org, an events service, and Flickr, a photo-sharing site.

Though Microsoft hasn't made notable Internet acquisitions this year, two weeks ago it announced it bought software and other assets from project-management specialist UMT. And Microsoft snapped up two Internet phone companies last year: Teleo and Media-streams.com.

In most cases, the Internet giants are acquiring software and other technologies to jump-start new product lines.

Teleo, for example, developed software that lets people make voice calls to land lines or cellphones by clicking on phone numbers on a Web page. Teleo also had been working on a service to initiate voice calls from within Microsoft Outlook and Internet Explorer.

Microsoft said Teleo would help it bring a new Internet calling service to market in partnership with MCI (now Verizon Communications) this year. Announced in December, the service will let people call regular phones through Microsoft's Windows Live messenger software.

Microsoft's other Internet-calling target was media-streams.com, a Swiss company that makes communication software that the software giant also plans to incorporate into its Internet phone products.

All the big Internet networks have been adding to their messaging technology to help people do advanced voice chatting and make calls from computers.

eBay made the biggest splash when it agreed to pay $2.6 billion for Internet-calling pioneer Skype Technologies in September. Yahoo! acquired Dialpad Communications for an undisclosed sum over the summer and in December announced it was adding Dialpad's computer-to-phone calling capabilities to its instant-messaging software. Google introduced the Google Talk service in August.

Voice calling could have significant advertising potential. The Internet companies hope their users will be able to search for restaurants, for example, then click directly from the search results to call for a reservation.

The software used to initiate Internet calls can allow for fancy call-control functions such as displaying caller ID on a computer screen, one-click dialing from an e-mail contacts list, or managing voice mail from within software menus.

Microsoft is preparing to roll out its own Internet search-ad engine, which is partly why many handicappers still see it as a contender.

The thing to remember, though, is that building 21st-century Internet networks is a lot like a real horse race — anything can happen on the next straightaway.

Leslie Walker is a technology columnist with The Washington Post.

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