you are not alone. I am exactly on the same situation... or even worse, at my work place thousands and thousands of nodes still runs older RHs with PHP 4 that I can't even think of updating it. Those clusters runs "modern" scientific applications that supports only RH platforms as they are shipped by default. If anything is touched / changed the application vendor won't provide any support anymore, even if that change has not to do with the app at all (e.g. PHP). The solution for me was to run my PHP applications only on control nodes (that is cluster monitoring nodes and etc.) with RHEL 5 and stick with 5.1.6, much better than PHP 4. But thats the best I can have for the moment.