First, as far as I can tell, there isn’t any way to create a new document (Word, Excel, PowerPoint) on the Smartphone itself. You can, however, edit a document brought over from a PC.
Second, as you may have read on the news-oriented mobile tech websites, you cannot work with files in the various Office 2007 formats (the ones that end in X like DOCX, XLSX, PPTX). You can, however, save files from Office 2007 to what Microsoft calls the 97-2003 file format that should be able to be used on by Office Mobile in Windows Mobile 6. And, the latest version of Dataviz’s Documents to Go features the ability to work with Office 2007 file formats (I haven’t tried this myself to verify this).