Apache Virtual Hosts and PHP 4

Hey gang, I installed PHP4 on my Apache server. It works fine on the default site however, I have 3 sites running off of my server using the <Virtual Host> directive. When I try to access a PHP file on one of the 2 other sites, it asks me if I want to download the file. Is there any way I can get PHP to work on all 3 sites? I suppose if worst comes to worst, I can always access PHP from the latter 2 sites by calling the first site but I don't really want to do that. TIA! jb