don't think thats the right way to use set interval

try this
weatherdat= function (){

_root.loadVariables("http://82.134.247.103/cgi-bin/weer/get.pl", "POST");

temp = searchandreplace(temp,",",".");
p=((Number(temp)+0)/maxTemp)*100
tmpbar._yscale=p
txt1.text=temp+"°C";

}
int=1000

setInterval(weatherdat, int);