Internet businesses are now center stage.

Microsoft President S. Ballmer moved his office from company_s main campus to the headquarters of Microsoft_s Interactive Media Group, the red-ink-stained unit down the road and across a highway. The move was more than symbolic. Ballmer, known for his high energy, make-it-happen style, is doing everything possible to convert Microsoft_s MSN.com into a profit center portal that competes with Yahoo! and America Online Microsoft has been working since last fall to build MSN as a brand name that unifies its Internet services, including Hotmail e-mail, Expedia travel, CarPoint auto buying, HomeAdvisor real estate and MSNBC news sites. Previously, each had its own identity, format and logo. Now, after months of tweaking, Microsoft is ready to move. An $18.5 million ad campaign to promote MSN is being launched Monday. Created by San Francisco agency Anderson & Lembke, the campaign includes newspaper, magazine and Internet ads; radio in key cities; and billboards in New York and San Francisco. TV ads are planned for later in the year. But Microsoft is building its Internet portal the same way it built the enormously successful Office software suite. It developed Word, Excel and other programs separately, then combined them into one integrated package. But unified passwords are not yet offered, MSN_s live chat Messenger service is about nine months behind , and other services, such as an on-line calendar, remain in the wings. The company is being extra careful because each new service has to handle all 35 million Hotmail users.