BM_Y_DIFF = 220;
BM_Y_TMP_DIFF = 220;
BM_Y_LIMIT = 200; // valeur à changer (voir aussi calque)
BM_SPEED = 20;
BM_DECALAGE = valeurDecal;
BM_LAYER = "nav";
BM_OBJ = document.getElementById(BM_LAYER);

function bodyMovinInit() {
	if (BM_OBJ != null) {
		bodyMovin();
	}
}

function bodyMovin() {
	
	if (window.XMLHttpRequest) {
		if(document.all){
			//IE7
			BM_Y_DIFF = document.documentElement.scrollTop + BM_DECALAGE;
		} else {
			//mozilla, safari, opera 9…etc
			BM_Y_DIFF = window.pageYOffset + BM_DECALAGE;
		}
	} else {
		// IE6, anciens navigateurs
		BM_Y_DIFF = document.documentElement.scrollTop + BM_DECALAGE;
	}
	

	if (BM_Y_DIFF < BM_Y_LIMIT) {
		BM_Y_DIFF = BM_Y_LIMIT;
	} else {
		BM_Y_DIFF += BM_SPEED;
	}

	if (BM_Y_DIFF != BM_Y_TMP_DIFF) {
		BM_Y_DIFF = (.1 * (BM_Y_DIFF - BM_Y_TMP_DIFF)) + BM_Y_TMP_DIFF;
		BM_OBJ.style.top = BM_Y_DIFF + "px";
	}

	BM_Y_TMP_DIFF = BM_Y_DIFF;
	setTimeout('bodyMovin()', 10);
}

if (isNavigatorOk()) {
	bodyMovinInit();
}