hi
I had similar problem with my n73, but turned out i had wrong version. Not sure what version i originally had but i copied the files to the memory card, using data cable and mass storage. But the program would not install and i could not find the tomtom icon.
Then i read somewhere i needed version 6 of navigator. So i downloaded and put that on the memory card. Once i disconnected the data cable the phone then did something automatically and installed it. Think it's cause this new version has an Autorun.inf file. I then went to Applications and there it was, TomTom icon.
I have version 6.010 (7640) installed.
I updated the firmware on my n73 few weeks ago,
v3.0638.0.0.1
30-10-2006
RM-133
Nokia N73 (39.01)
Hope this helps