Using PHP4 or PHP5

As I mentioned earlier, I am putting a team together to create a web-based RPG, different from the one I am currently playing. Would it be better to use PHP4 with it's strong developer base, or the new PHP5 which is more object oriented an in my opinion would be easier to keep the game up to date? -- Michael Lauzon P.S. This is the game I am playing, but I have ideas that I think can be done better than what was done for this game -- but everyone always says that!: http://phantasyrpg.com/main.php?view=9898