Although Microsoft (NSDQ: MSFT) hasn’t made its plans to sell interactive ad shop Razorfish official, sources say the company has been stepping up preparations for the sale of the aQuantive unit recently. And that’s in spite of concerns that Microsoft wouldn’t be able to get the price it wanted. Microsoft has reportedly backed off the earlier asking price of $800 million and is now willing to accept between $600 and $800 million. And while the number-four ad-holding company Publicis Groupe is in the lead, that doesn’t mean that two other potential suitors—WPP Group and Aegis Group—are out of the running.

—A long time coming: A number of observers I talked to said that they’ve been surprised at how long its taken Microsoft to try to get out of the agency business—an area the company didn’t intend to get into when it bought aQuantive for $6 billion nearly two years ago. The Redmond software company wanted aQuantive so it could offer ad-serving platforms that could compete with Google (NSDQ: GOOG) and DoubleClick. Initially, Microsoft tried to persuade aQuantive’s then-CEO Brian McAndrews to cut out Razorfish from the deal. But he refused, saying it was an all-or-nothing deal and so, Microsoft reluctantly agreed.

—Publicis vs. WPP?: In a sense, Publicis seems like a much more natural fit for Razorfish than its current home. The Paris-based agency company kicked off 2007’s digital M&A frenzy when it acquired Digitas in December 2006. That unit has been at the center of Publicis CEO Maurice Levy’s goal to make interactive a larger part of its bottom line. And he has loudly and repeatedly said he is still prepared to spent more to make that a reality sooner than later. And so, Publicis has replaced WPP Group as the expected suitor for Razorfish, as it would make a nice addition to Publicis’ digital hub, VivaKi. Interestingly enough, VivaKi just inked a major deal with Microsoft on targeted TV ads, representing a bridging of the traditional and digital. WPP had hoped to arrange a swap with Microsoft last summer involving online ad management system Open AdStream, which WPP got as part of its $649 million acquisition of 24/7/Real Media in May 2007. For one thing, WPP has mainly been looking at small digital acquisitions in emerging markets lately and some analysts believe the agency doesn’t have the wherewithal to do a major digital purchase right now. Still, WPP CEO Sir Martin Sorrell has defied conventional wisdom before and once he’s set his sights on a target, he rarely lets it go without a fight.

—Other contenders: Aside from those two serial interactive acquirers, Aegis is another company that’s considered likely to challenge Publicis for Razorfish. While that UK holding company has been snapping up digital firms at fairly steady clip for the past year, it’s main focus is media buying and search. While Razorfish might be a good way to expand its digital capabilities, it’s unclear with the company would be willing to make sure a big acquisition, especially as it’s mainly been making smaller buys in Asia and Latin America. One industry observer I spoke to thinks that a buyer could come from the private equity side, perhaps a company like General Atlantic, which took a majority stake in interactive firm AKQA in Feb. 2007. But with Razorfish’s work on ramping up its creative bona fides in the past year, the ability of an ad firm to buttress its traditional skills with new media would be very valuable, even as the ad business struggles with a pullback in client spending.

• Microsoft To Sell Razorfish; Publicis Groupe Possible Bidder
• To Bundle Digital Or Not Bundle? Agency Debate Continues