Backpacker is right. This has already been widely discussed in the airline sections of pprune in connection with the Cypriot B737 depressurisation incident, and others (so it's no secret). The cockpit can be accessed from the outside and at least one member of the outside crew knows how to do it. It doesn't involve forcing the door or anything like that.
Sternone - the UK pilot mags will print any old rubbish and the quotes you gave are a fine example. In any case, nobody would (in that situation) be trying to set things up for a Cat 3C approach; one would fly it manually, and a 747 will fly manually just fine. Nearer to a landing, one would slow down to say 250kt which is only a little faster than a decent IFR tourer, and I've seen ground speeds well above 200kt in a descent from say FL150 with tailwind.
If the competent private pilot had next to him a really dedicated FS2004/FSX sim player, they could do quite well. Many sim types fly real routes (which they check against Eurocontrol, believe it or not), real STARs, approaches, the works. They even use real ATC, provided (over the internet) by current or retired ATCOs.