NameVirtualHost breaks PHP

Hello. I'm new to this list, though not new to PHP. I'm hoping that my question hasn't been answered a thousand times before, and I did at least search on NameVirtualHost and read all those archived messages before getting to this point. I have an Apache web server (1.0.38) that has been peacefully co-existing with php4 for quite some time. I've interfaced it to mySQL, and life was great. Then, I came up with the brilliant idea to used Named Virtual Hosts rather than using up all my IP addresses. I did all according to the instructions I had, and the "virtual" part of things worked fine. www.hostone.net showed its proper page, as did www.hosttwo.net. But.... It broke php. When I go to a php page now, it show's the code rather than executing it. I've verified that this behavior happens across all the web pages, incuding the "main" one that isn't "virtualized." Can anyone point me in the right direction? Thanks in advance.