Hi Rodik,

What is your planned application in car?

If you are planning to monitor movements (i.e alarm use), then placing is not a problem. You can reset acceleration/tilt values for interrupt at any angle.
If you are keen to know real acceleration values in all axis, then IC need to be at level, X&Y=0, Z=90. Bit more demanding, but ... Constant tilting will give static values.

Values need to be read from IC via I2C, so if constant reading is needed then you have to do reading loop for that purpose. Data can be put to serial port as well as to LCD, so that is no problem. You have to adjust output part of the code.

BR,
-Gusse-