swaping the weapons

I have two gun i want to swap between the these two guns when in press space bar like real game.In my game it is first person when i press space bar these two weapons should swap each other

From the Unity3D FPS tutorial part2 page4:

function Awake()
{
    // Select the first weapon
    SelectWeapon(0);
} 
function Update()
{
    // Did the user press fire?
    if (Input.GetButton ("Fire1"))
        BroadcastMessage("Fire");
    if (Input.GetKeyDown("1"))
    {
        SelectWeapon(0);
    }
    else if (Input.GetKeyDown("2"))
    {
            SelectWeapon(1);
    }

}

function SelectWeapon(index : int)
{
    for (var i=0;i<transform.childCount;i++)
    {
        // Activate the selected weapon
        if (i == index)
            transform.GetChild(i).gameObject.SetActiveRecursively(true);
        // Deactivate all other weapons
        else
            transform.GetChild(i).gameObject.SetActiveRecursively(false);
    }
}

This function detects keyboard input; the fire button, the “1” button for weapon 1 or
the “2” button for weapon 2. The weapons will be children objects of the Main Camera.

Hope that helps.
If you still have trouble, get the tutorial from http://unity3d.com/support/resources/tutorials/fpstutorial.html and do it.

You could do something simple like:

var weapon : boolean = false;

function Update ()
{

if(Input.GetButton(“space”) && weapon == false)
{
weapon = true;
}

if(Input.GetButton(“space”) && weapon == true)
{
weapon = false;
}

if(weapon == true)
{
“this would be where the user see’s the first weapon”
}

if(weapon == false)
{
“this would be where the second weapon goes”
}
}

And you could do something like this for the animation of switching weapons
if(Input.GetButton(“space”)
{
“play switching weapon animation”
}

Hope it helps!