Migration from php4 to php5

I'm going to move my PunBB 1.3 forum from server running php4 to a server running php5.

Will I have to make any changes/ajustments to scripts, configuration, etc.?

Forum currently uses "File based (fancy)" URL scheme, if that matters.

Also, current server is Win 2003 with Apache module, the new one is Linux 2.6. I guess I'll have to chmod manually certain folders -- unless there is an easier way to do that. (Is there?)