minisd is just another type of memory card, available from all good memory retailers
you need to use Tom Tom Mobile, if you have a look at their website you will see all the different versions. If you have a look at Tom Tom Mobile, you will see that you can buy it with or without the bluetooth gps receiver and on a cd or on a memory card
it is relatively easy to install if you choose the cd option but you will need a card reader that supports minisd. basically you pop the memory card in the reader, plug the reader into your pc (normally usb) then it appears as a removable drive. copy the tom tom folders to your removable drive, then unplug the reader, take the memory card out, put the memory card back in your phone and switch the phone on. the tom tom icon will appear in you nokia menu as if by magic