My problem is that I would like to send the data using programming language through the USB port and then display the result on the board's LED display.,I would like some hints on:
1. what programming language best fits on my project?
2. how can I send data through the USB port to arduino ? i'm using Arduino Diecimilia ver 1.0

plz. reply ., i'm running out of time.,

 

>>1. what programming language best fits on my project?
Just use the arduino programming language.
>>2. how can I send data through the USB port to arduino ? i'm using Arduino Diecimilia ver 1.0
Simply use the Serial.read command to read the data you pass it via the serial port monitor built into the Arduino IDW

It can't get any easier as your project is 100% completed here (assuming you want an 16x2 LCD readout)
http://arduino.cc/en/Tutorial/LiquidCrystalSerial