problems with php4 and apache

Problem Running a redhat 6.1 server, using apache, ssl mod, mysql, and php4. everything compiled together nicely, and it seemed to work. then the client uploaded thier php enabled webpages, and nothing is going on. no pages are displayed, and the server evidently does not read the html pages that contain the php data as having anything on them. some of the developers are using the short script header "<?," and some of them are using "<?php" headers could this cause problems in the scripts (they have written other sites using the same combination with no problems.) thanks, Madoc