The Boeing 747 Jumbo Jet is my favourite aircraft of all, even after the Concorde! It is so huge (around 400 tons fully loaded!) and yet so graceful. I will add further to this page when I can
You can fly a 747 in the X-Plane flight sim. You can set any fuel or pax/load weights, and fly any spec 747, from the original -100 to the latest glass cockpit -400 series. There are even prototype 3 engine and extra large versions available to fly.
There are 3rd party add-ons for Fly! including full featured cockpits of Boeing 757/767/777 aircraft. Hopefully when 4 engines are included in Fly! a 747 will be included. In themean time you can use the excellent 747 Precision Simulator (windows only) which recreates a full 747 glass cockpit, including FMS and full navigation features.