sunfighter : Well, I may have given a bit of a wrong impression with my initial post. There already exist many lines of PHP code and with each request, the tasks are done server-side. What is left on the client end of things is to a) execute the additional tasks the PHP scripts tell me to, simply by requesting other urls in the proper order as well as keep doing that until everything is done and b) to display the results of said tasks properly in the browser.
rnd me has done just that and I'm very grateful for his suggestion to use callbacks. I'll be making myself familiar with the concept and then attempt to build it the right way, without loops, frozen browsers, etc
Thanks for your help!