If the enemy of my enemy is my friend, then maybe Microsoft execs will be sitting down with Google's management in a few days, now that Yahoo is teaming up with eBay to take on Google.

Microsoft, of course, has targeted Google as the leading threat to its continued hegemonic existence in the world of personal computing. Simultaneously, three of the four companies mentioned here are emerging as major media companies, with eBay always wary of encroachment by the new media titans on its core garage-sale business.

Yet the geometry of the situation may change now that Yahoo and eBay have announced a multi-year "strategic partnership" with four major components: search (along with graphical advertising), online payments, a co-branded toolbar, and the emerging "click-to-call" functionality. The companies said their agreement will be fully up to speed in 2007. The agreement is clearly aimed, by Yahoo at least, at attacking the No-Evil company's leadership in the vast and still-burgeoning search market; but it must also represent a renewed threat to Redmond as well.

According to terms of this agreement, Yahoo "will become the exclusive third-party provider of all graphical advertisements throughout the eBay.com site, and sponsored search for complementary products on some eBay.com search results pages in the U.S.," according to a company statement. The two companies will also work to optimize eBay listings within Yahoo searches, as Yahoo tries to retake leadership from Google in the search territory it pioneered.

Yahoo CEO Terry Semel said the agreement will let the company "further extend our sponsored search and graphical advertising reach to one of the largest and most active communities on the Web." For her part, eBay CEO Meg Whitman (pictured above) said "this agreement represents a great opportunity to benefit our communities and grow our businesses."

The payment system will be the technology industry's latest effort to develop effective "online wallet" program, and aims to give people the ability to pay for Yahoo services from bank accounts, credit cards or balances in PayPal accounts. Yahoo says PayPal (which is of course owned by eBay) will be "deeply integrated" within the Yahoo site. (Now if the two companies could launch a global initiative to eliminate eBay and PayPal spoofing scams, they might have something.)

Effective online payment systems have been a prized goal of Internet-based companies for the past decade. The lack of a truly automated payment system was a major impediment to revenue generation during the dot-com bubble, in this observer's opinion. Secondly, an industry failure to create effective "micropayment" schemes established, seemingly forever, the concept that Web content should always be free, a reality that continues to impinge upon the business models that can be developed for Internet-based businesses. In any case, Yahoo and eBay will be working the first part of this problem in their new agreement.

The co-branded toolbar will integrate Yahoo search and site links (including mail and My Yahoo) into a version of the eBay toolbar, according to the new agreement.  The companies say the eBay toolbar has been downloaded by more than four million eBay users to date.

On the click-to-call front, the companies plan to let those who are interested to work through Yahoo Messenger and Skype to reach advertisers in this program directly. It's a Calling Avon world rather than an Avon Calling world.

The two publicly-traded companies have said they do not expect the agreement to have a material impact on their financial results in 2006--which either implies they won't be spending much, they will bury the costs in ongoing operations, or that they quietly hope for a nice surprise in revenues--but did say they will "incorporate any financial impact for 2007 and beyond when they deliver their business outlook for those periods."

Meanwhile, does this mean Eric Schmidt and Steve Ballmer will suddenly become good friends?