Yes it's possible. What you'd want to do is create a PHP file which will successfully open the url, grab the contents of it, and save it in a new file somewhere on your system (so you'd want to use [man]file_get_contents[/man] and some [man]fopen[/man] and [man]fwrite[/man] functions 😉 ).
Then to get it to run at a set interval (however often you wish) you'd need to set up what's called a "Cron Job" or "daemon" in other systems. This will automatically run your script at whatever interval you specify (every hour, every 3 hours, every day, every week, once a year, etc.).
That's pretty-much it. The only thing you'd need to watch out for is if the URL you're trying to get fails to load for some reason and you write blank data to your xml file.
