Yes my host 1&1 internet runs php4 by default - I have spoke to them on the phone this last half hour
That seems a bit mad to me but anyway they said if I create a file called .htaccess
and add a line
AddType x-mapp-php5 .php
and ftp this to the root folder of my site then it will switch to running php 5
I was a bit surprised to hear this is needed myself!
They also have this information
PHP5 has register_globals, allow_url_include and allow_url_fopen all disabled by default which may cause improper functionality for some scripts when switching from PHP4 to PHP5
I'm not sure if that would affect my very modified vbulletin 3.7 based site - the test version of the site runs OK on php 5.0 but how do I check these settings on my test server to see what I have set there?