How would I go about pulling in tweets from multiple twitter users with PHP and displaying them as part of one combined list on my page?
Use the search API and boolean OR operator. For example here is the URL for CNN Breaking News and NPR All Things Considered:
http://search.twitter.com/search.json?q=from%3acnnbrk+OR+from%3anpratc
The query is URLEncoded so use Fiddler Tools -> Text Encode/Decode or your favorite tool to see that the correct format in plain text is:
q=from:cnnbrk+OR+from:npratc
Hope that helps.
You can also create a list of the accounts you are interested in and place a list widget on your page. No PHP needed.
http://help.twitter.com/entries/76460-how-to-use-twitter-lists
http://twitter.com/goodies/widget_list