Earl00 is right - read before asking...

The Nokia n800 runs Linux, but basically needs programs already ported to run on it (some exceptions, mainly command-line programs). Lots available at http://maemo.org/

As for Word/Excel, I've installed the Mozilla-based browser and use Google docs - works great for that quick read of a Word attachment.

You can tether the n800 via a 3g phone - I use USBModem on my Treo 700p - works great! Many phones work out of the box - you cell provider may want $$$ YMMV