IBM has locked horns with Microsoft over everything from operating systems to database software to e-mail programs. In recent years, IBM has backed the uprising of the Linux operating system, pushing the community-built software while Microsoft pours hundreds of millions of dollars into developing its next version of Windows, code-named Longhorn. Now, the two tech titans find themselves competing again, this time in the hottest new markets for collaboration software -- programs that serve up secure instant messages and Web conferencing services.

To this battle, IBM brings two key weapons -- its long-popular collaboration program, Notes, and its new package of applications, Workplace. Notes has long been a way big corporations help workers create virtual workspaces for teams to share and modify documents. Launched last year, Workplace lets companies customize employee computing environments, shooting specific programs that workers need right from a computer server to a Web browser on their PC. And since Workplace is browser-based, it can work on Linux as well as Windows.