PHP & jQuery

PHP & jQuery

I hope the following makes sense.

How would I take a value stored in a variable in PHP, do a post or get to another php file (the function that checks to see if the pc is alive), and have it display the results in some CSS box? 

If you can point me out to any examples that you know, or to the various functions in jQuery I will need. 

I looked at the jQuery.get page on this site, but it is not a thorough enough example for me. I don't even know if that is the right one to use. 

Thank You.