depends if you want a genuine copy or not?
List of things needed:
1. Bluetooth GPS Reciever - from ebay
2. Minimum 256MB RS DV MMC card
3. TomTom Mobile 5 Software - Bought from shop or online which enables you to TomTom traffic and weather etc... or downloaded using Torrents however doesnt allow you to use the above features.. but you can get any maps you want for free.
4. In Car Holder - Otherwise its a pain in the arse
5. In Car Charger - TomTom program eats battery time so useful to charge on the go.
Thats it really
To Install:
Put mmc card into a card reader, copy over the tomtom folder and other stuff and then put in phone and your done.