It's not going to be until AFTER the next version of Office for Windows, "Office 12", is released... and that's scheduled for later this year, when Windows Vista is released.
So realistically you're looking at 2007 at the EARLIEST for the next version of Office for the Mac. But I believe that Microsoft is working on Universal Binaries for Office 2004, and they should be out before too long... and you can still run Office 2004 on an Intel-based Mac using Rosetta emulation.