It depends a bit on how your world is oriented along the axis, but basically change the transform.forward to transform.right (and for other way negate power) and you probably are shooting in the right direction.

Okay, without doing anything smart the code would end up something like:

var Char_Bullet : Transform;
var power = 2000.0;

function Update () {
    if(Input.GetKey("j")) 
    {
        var bullet =
Instantiate(Char_Bullet, GameObject.Find("Gun_Spawn").transform.position, Quaternion.identity);
        bullet.rigidbody.AddForce(transform.right * -power);
    }
    else if(Input.GetKey("l")) 
    {
        var bullet =
Instantiate(Char_Bullet, GameObject.Find("Gun_Spawn").transform.position, Quaternion.identity);
        bullet.rigidbody.AddForce(transform.right * power);
    }
}

That helps to shoot to the right. This still leaves shooting to the left not working. Could you please explain how to negate the power? Because simply making it less or even a negative, it just randomly sprays the bullets.