"KOffice is much more lightweight," Kugler said. "One often hears that OpenOffice's codebase is quite complex and rather large. While KOffice is lacking some functionality compared to OpenOffice, it's certainly catching up - and eating less valuable developer time in the process."
It isn't ready just yet, with a tentative launch date for the first half of next year. Their competition is really cut out for them – Microsoft reigns supreme in the office world, and OpenOffice has matured greatly in its development.
Still, the more the merrier, usually. The buck doesn't stop with KOffice running under Windows, with some aiming to make many KDE apps very portable:
Having KDE applications run on Windows of course also makes a lot of sense for enterprise users [as] they don't have to support one client per operating system that might be used in the company, but they can standardize on, for example, KMail as a PIM solution."
You can read more about it at the KOffice site