Redmond, Wash.--Microsoft Corp. Thursday said it agreed to acquire Great Plains Software Inc. for $1.1 billion. Great Plains makes so-called enterprise resource planning software--though, unlike ERP giants SAP AG and Oracle Corp., Great Plains is focused on small to midsize businesses. It's an intriguing move for Microsoft, which has partnered with b-to-b vendors such as Commerce One Inc. and Clarus Corp. to support their Windows-based applications. But the Great Plains deal represents the first time it will sell a complete, prepackaged business application. As important as the Windows operating system is to Microsoft, its biggest cash cow is perhaps its Office software suit. The Great Plains applications target the same market, but are focused on e-business rather than basic office functionality.