Microsoft has released Office Mobile 6.1, which includes support for Office 2007 file formats. You've waited a year since Office 2007 went RTM, so hop over here and download it now. It works with Windows Mobile 5 Pocket PC Edition and Windows Mobile 6, so if you've got a WM5 SmartPhone, well, you're out of luck.
Microsoft lists other improvements to Office Mobile 6.1 including:
• Enhanced viewing experience for charts in Excel Mobile.
• Ability to view SmartArt in PowerPoint Mobile.
• Ability to view and extract files from compressed (.zip) folders.
I'm currently stuck with a WM5 Moto Q, but my new Sprint Mogul should be in any day now, so I'll be testing it out soon.