find, getcomponent, yourfunc -> ERROR "is not a member of 'UnityEngine.Component'. "

if you want to call other object script,
別のオブジェクトを検索して、そのオブジェクトの関数を呼びたいとき、

you should declare script name explicitly.
取り付けたスクリプト名を明示的に宣言しましょう.
another object ... myGUI
and attached script to myGUI ... guiscript.js
//ERROR
var spawnParticle : ParticleAnimator;//particle etc
//var guiScript : guiscript;

function Update () {
}

function OnCollisionEnter(theCollider : Collision){
 if(theCollider.gameObject.tag == "bullet"){
	 generateParticle();
	 Destroy(gameObject);
	 resetGui();
 }
}

function generateParticle(){
	var obj = Instantiate( spawnParticle, transform.position, transform.rotation);
	obj.autodestruct = true;
}

function resetGui(){
	var obj = GameObject.Find("myGUI");
	var guiScript = obj.GetComponent("guiscript");
	guiScript.reset();
}
//It works!
var spawnParticle : ParticleAnimator;//particle etc
var guiScript : guiscript;

function Update () {
}

function OnCollisionEnter(theCollider : Collision){
 if(theCollider.gameObject.tag == "bullet"){
	 generateParticle();
	 Destroy(gameObject);
	 resetGui();
 }
}

function generateParticle(){
	var obj = Instantiate( spawnParticle, transform.position, transform.rotation);
	obj.autodestruct = true;
}

function resetGui(){
	var obj = GameObject.Find("myGUI");
	guiScript = obj.GetComponent("guiscript");
	guiScript.reset();
}