simple desktop (Score 1)

IMHO. Your best bet would be KDE if you insist on Linux. It's a stable platform. You can configure a simple desktop for your grandfather with shortcuts to ease access to his favorite programs. It also has easy Internet browsing built in just in case Netscape is too much for him. It's is very easy to use and very easy to customize. While I'm not a big Windows fan. It's still the simplest OS for the average user on the PC. But it can also be as complex as X/Linux.