LEGO Hidden Side Sets

Is it hard putting motors in Lego trains? do you have to rework and get special blocks for the inside and wheels?

These days you can get a bogey with a motor/wheels in it, this connects to a power box and an IR receiver.  These usually fit fairly easy, in fact some manuals for example the Christmas train actually tells you in the manual how to modify the build to fit them.

Mind you this year they've brought out a new system that replaces this older IR controlled version, I'm not quite sure how this works but it may be Bluetooth for the controller...