PHP4 vs PHP5

Hi I know this topic has to be discussed several times but I have a situation I need some advices. I am working in a small company. The company does everything you need. Computer service, sell computers, install servers, web page, etc. I am in the web department. The guys from the server installation and that stuff are using a modified debian, which for default in his stable release has php4 and apache 1.33. I am new at the company and I have to decide what I need and what I am going to do. My choice is to use the CMS Mambo and make the modification that each client would ask. So I've seen that php5 has a lot of cool staff, like mysqli and the new (and faster) object oriented thing. I would like to know if it is "safe" to use this version. I know that mambo use objects so I think that php5 will do a better job running it. I also think php5 (or php6) is the future we can use php4 for ever. So whats your opinion? Thanks A last comment: I apologize for my English, please let me know you didn't understand something -- yo@fernandocosso.com.ar http://www.fernandocosso.com.ar