Filed at 12:30 p.m. ET

REDMOND, Wash. (AP) -- Kevin Browne, the general manager of Microsoft Corp.'s Macintosh Business Unit, is leaving to work for Xbox, Microsoft's video game division.

For three years, Browne led the 145-person team within Microsoft that develops applications to run on Apple's Macintosh computer platform. Microsoft has not named a replacement.

The company did not specify why Browne is leaving the division, beyond saying that he will have the opportunity to learn new skills and ``pursue his personal interests in games and sports.''

But sales of Microsoft's Office v. X for the Mac have been disappointing, said Rob Helm, research director for Directions on Microsoft, a Kirkland-based independent research firm.

In July, the company announced sales of 300,000 since its release in November, less than half the 700,000 it had hoped to sell by that point, he said, and some at Microsoft said Apple was not efficient in marketing its newest operating system, OS X.

The two companies have since announced a joint promotion to market Apple's operating system and Microsoft's business software.

``He got handed a tough job,'' Helm said. ``It's just not at the moment a great career move to be running the Mac unit.''

Browne was unavailable for comment, a Microsoft spokeswoman said. Apple Computer Inc. declined to comment.