While you can edit Word and Excel files in Windows Mobile 6 devices, the New Word Document and New Excel Document options are missing from Windows Mobile 6 Classic (ie. Windows Mobile Smartphone, such as HTC 621, T-Mobile Dash, etc).
You have couple of options:
1. Keep a copy of empty Word and Excel docs on your device, copy and rename the files when you need a new document.
2. Buy Documents to Go from RoadViz, it even supports Word and Excel 2007 docs.
3. Use this nifty app called MoDaCo DoNew.
See http://www.modaco.com/index.php?showtopic=252990 for more info and download