All you do is mount the desktop's CD or hard drive on the Duo's desktop and install from there. It's slow but it works just fine. NewsWatcher of course for news. Excel 5.0 works, but 4.0 would be better on an '030. Believe me, they've published glossy magazines with a lot less.
All Duos have a slot for an optional internal modem.
You can certainly surf the net and fax at this speed, but it won't be fast. If you're using the Duo in desktop mode, maybe think about an external 33.6 or 56K modem to plug into the serial port. But whatever anyone says about fast modems, 19.2 is fast enough to get a bit of work done. And then they were. The PPC Duo upgrade is a full logic board upgrade .