Hi Alvaro,
If I understand your first question correctly, you want to print your number in decimal on the LCD.
See the section "Printing Numbers" on the LCD wiki page:
http://www.arduino.cc/playground/Code/LCD
Remember that the LCD library print() functions accept single ascii characters or strings of characters. So first you have to convert your number into a string representation. The wiki section above shows how to do this using the itoa() function.
It might make sense for the LCD library to provide another function, say printNumber(int) which took an integer and printed its string representation in decimal.