Best way would be to use some api made available by the author of a page. Usually it's done with SOAP. This way is quicker it's obvious that the author of a page agrees to share the content (because he had to prepare the api).
Another way is to rea a page with file_get_contents() and match the data you're looking for (with regex and [man]preg_match_all[/man]). This takes more time (as all the page, with formatting has to be read and matching takes time too). And there is strong probability that you don't have permission to use the content from the other site.
