self.resizeTo(("800"),("600"));
x = screen.availWidth;
y = screen.availHeight;
x = (x-800)/2;
y = (y-600)/2;
self.moveTo(x,y);

function fermer_fenetre()
{
	document.write('<form>');
	document.write('<input type="button" value="Retour au site" onclick="self.close()">');
	document.write('</form>');
}