As far i understood you want to make a Ajax Timer which periodically run and Update a Section of the page based on the response received.
This is very well done through
setInterval(func-name, interval-span);
.
your code seems same what you want. check the following lines.
loadXMLDoc();
setInterval(callServer, 30);
callserver is not a function you should call
loadXMLDoc
here
loadXMLDoc();
setInterval(loadXMLDoc, 2000);
If it doesnt help please describe your problem with more detail.