I have not done this yet but I have an idea of how you would need to do it.
First you are going to need to use fopen to open the other page and place the contents of that page into a file for your script to read.
You will then need to search that file for the occurrence of the specific div span element that you are looking for. I hope for your sake that the span you are looking for has a specific name and not just span hehe. Anyways you do the string search find what you are looking for and then slap that into your variable.
Helpful links:
http://us2.php.net/manual/en/function.fopen.php
http://us2.php.net/fread
http://us.php.net/strings
Since I do not know the specifics of what you want to do in terms of finding the term the third link is to all PHP string functions.