Double Interfacing?

I am working on a project where my Arduino must be able to send and recieve commands from a laptop, and send commands to an LCD. I've heard, however, that the microcontroller can only interface with one serial device at a time. Is this true? If not, how do I do it?

Define 'at a time'

I mean both the laptop and LCD must be connected, and the Arduino needs to know which one to send it to.

What i mean is what code do I use to send a message to, say, pin 0 as opposed to the serial port connection, or vice versa.

Pin 0 is the serial port (or at least half of ot)

Right, as people are being hard on you I'll be nice.

Pins 0 and 1 are the pins used for the hardware serial port (USB).
On the Arduino mega you get 3 additional hardware serial ports which you can use for serial connection to devices.

On any other board you can use softwareserial (newsoftserial) which is a library designed to allow you to use any pins as serial port pins.

Mowcius

I am working on a project where my Arduino must be able to send and recieve commands from a laptop, and send commands to an LCD.

In addition to using a Arduino Mega or the SoftwareSerial Library, you might also considering a LCD that uses I2C or SPI. They tend to be a little more expensive but you don't have to worry about overlapping the serial ports.

Also, ATmega644P, used in Sanguino and Duino644, offer 2 hardware serial ports.