As Q stated above, it's basically plug & play.
However, you do need to move the skinny, black antenna cable from the seperate trimble unit (which is now not needed & can be removed once your MKIII is installed) & plug it into the back of your MKIII.
The MKIII (& the MKIV) both have internal trimble units, while the MKII has an external trimble unit.
2000 740iS. MKIV, 16x9, DDEs controlled by Euro fog light switch, reversed steptronic +/- pattern, paddle shifters, clear corners, Basslink, iPod video with stereo audio, TV tuner, gauge rings, ///M pedals, backup camera with 'on demand' switch, quad brake lights, Dinan engine & tranny software, windows/sunroof close via remote.
2003 540iS. MKIV, 16x9, PDC, CWP, TV tuner, backup camera with 'on demand' switch, paddle shifters, windows/sunroof close via remote, iPod video & audio.