What you could first do is create an array for the player's weapons (in a weapon control script similar to the one in the FPS Tutorial). That would allow you to have two easily switched out weapons and leave the option the increase the number of weapons easily. This script would manage the weapons as well as tell them when to fire/reload and would be added to the main camera of your player (the weapons themselves would be children of the main camera). The weapon scripts would have functions called "selectWeapon" and "deselectWeapon" to turn them on or off.

    var weapons : GameObject[]; 
var selectedWeapon : int;
function Start () {

// Select the first weapon
SelectWeapon(0);
}

function Update () {
if (Input.GetKeyDown("1") && !(weapons[0].gameObject.GetComponent("weaponlocking").isLocked)) {
    SelectWeapon(0);
    selectedWeapon = 0;
}   
else if (Input.GetKeyDown("2") && !(weapons[1].gameObject.GetComponent("weaponlocking").isLocked)) {
    SelectWeapon(1);
    selectedWeapon = 1;
}   
    if (Input.GetButtonDown("Reload"))
        BroadcastMessage("Reload");

}

function SelectWeapon (index : int) {
    for (var i : int=0 ;i<weapons.length; i++)  {
        //select the weapon
        if (i == index){
        weapons[i].gameObject.BroadcastMessage("selectWeapon");
    // Deactivate all other weapons
    }else{
        weapons[i].gameObject.BroadcastMessage("deselectWeapon");
    }

}

What you could then do is create a "selectableWeapon" script, which would only need to have one variable (the weapon that it references). You would put this script on the weapon model in the environment and then tag it as something like "pickupAble" (so that when the player looked at the weapon lying on the ground they can pick it up).

var weapon : GameObject;

You would just need to have every possible weapon be attached to the main camera (all but two of them being deactivated), so that when the player selects a gun off the ground that weapon would activate one of the player's weapons. Here's a "selectweapon" script that you could put on the main camera to actually switch the weapons out.

function Start (){
        //playerWeapons is the weapon controller script from above
    playerWeapons = this.GetComponent("playerweapons");
}

function Update () {
    //this draws a ray to check if the player is looking at a selectable weapon. It would also be possible to use OnMouseOver unless you have a texture in the middle of your screen (textures block OnMouseOver so if you have a crosshair you can't really use it)
ray = transform.camera.ScreenPointToRay (Vector3(Screen.width/2.0,Screen.height/2.0,0));
if(Physics.Raycast(ray,hit,100)) {
    if(hit.collider.gameObject.tag == "pickupAble") {
        selectedWeapon = hit.collider.gameObject;
    } else {
        selectedWeapon = null;

}
if(selectedWeapon && Input.GetButtonDown("pickup")){
    for (var i : int=0 ;i<playerWeapons.weapons.length; i++){
        if(playerWeapons.weapons[i] == selectedWeapon.GetComponent(SelectableWeapon).weapon)
            return;
    }

    playerWeapons.weapons[playerWeapons.selectedWeapon].gameObject.BroadcastMessage("deselectWeapon");
    playerWeapons.weapons[playerWeapons.selectedWeapon] = selectedWeapon.GetComponent(SelectableWeapon).weapon;
    playerWeapons.SelectWeapon(playerWeapons.selectedWeapon);
}
}

These are trimmed down scripts from my game, so they would require some tweaking to work in another one. Again, though, a lot of this is derived from the FPS Tutorial if you want to look at that. Also, sorry if this is too long or too specific.

Can u help me with the weapons pack from you? , its says that the Reload input and the pickup input is missing how do i add it? i download your pack