Actually when I installed php5, it was switched off (using the recommended php.ini settings). But I've checked with my webhoster and they will set this parameter to on. I've checked my scripts and they are all fine now, so my problem is solved for now
My webhost has announced they will upgrade to php5/sql5/apache2 next month (currently php4/sql4/apache1.3).
I have created a test environment to check if all my scripts remain working, and already upgraded my guestbook to Lazarus 1.5.4 (thanks Carbonize for this great script!).
I'm also using the advanced poll (v2.0.3) on my website, but it gives all sort of problems (probably the HTTP_SERVER_VARS stuff, which is not allowed with the new php5 config). I downloaded the newest version of advanced poll but it looks like this has not changed.
Does anyone have experience in getting advanced poll to work under php5?