I think you need to change your idea of what "AJAX" is. It's not a method to update the content of a <div>. It can be used for that, but so so much more.
It's a method of transferring data from one side to the other.
If you think of it like that.. of course it's possible to update the content of two areas in the DOM. You just need to send that data down to the client is such a way that the code receiving it cat separate it and know where to insert what.
It is a tricky situation. The typical AJAX sample code usually creates an XML request object and then sets a handler that responds to status changes. The function will finish execution before the XML object receives data back from the server, so you need to keep your request variable at a higher scope than the calling function. If you simply call the function twice, you will replace the contents of the variable with a second XML object before processing the return status of the first function call, therefore you will need a second variable at a global scope to process two requests at the same time, and you'll need to pass the XML object variable as a parameter to the function that sends the request and attaches the event handler to it.