Scrambling to buy a place in interactive advertising that it’s been unable to reach through its own ad network, Microsoft announced it would pay US$6 billion in cash, the biggest acquisition in Microsoft’s history, for aQuantive.

If the purchase is approved, it would help Microsoft expand its advertising network on the Web, mobile phones and IPTV, as well as XBox Live. Though it owns one of the most popular websites, Microsoft’s web search traffic still trails Google and Yahoo.

aQuantive’s biggest division, Avenue A | Razorfish, is one of the world’s largest interactive ad agencies. It’s most profitable division, Atlas, makes the Media Console advertising platform that measures the effectiveness of ad campaigns, while DRIVEpm, matches advertiser campaigns with publisher inventory.

The deal closely follows Microsoft’s purchase of leading European mobile advertising company ScreenTonic. 

aQuantive of Seattle, has about 2,600 employees, and had 2006 sales of US$442.2 million, US$54 million of which was profit.

Microsoft is paying an 85% premium for aQuantive. After the announcement, aQuantive shares jumped almost 78% percent on the Nasdaq stock market.

 ValueClick, one of aQuantive’s few competitors that hasn’t already been bought out by a larger company, bounced to a record US$31.59 per share. Global Crown Capital analyst Martin Pyykkonen estimates ValueClick could sell for US$4 billion or more. Or if buyers wanted ad serving technology instead of an ad network, they might move to acquire the Viewpoint Media Player.

Advertising mergers and acquisitions in new media since March have included some promising mobile advertising companies, such as Third Screen Media, ScreenTonic, and 24/7 Real Media. We guess the purchase of aQuantive means there won’t be a Microsoft/Yahoo merger.