I take i that they are NOT compatible? We moved to a new ISP and dedicated hosting server, but they have PHP5 on the system and MySql 4.1. After all that transfer and upload, all pages come up blank

The ISP will revert back to a lower version of PHP, but then they said they will nto support it if we did?? Is there ANY type of work around or did I kust lose everything I have??
Is it also possible to load a vanilla PHPBB which IS compatible with PHP5 and keep my forum structure and data??
Thanks in advance!!
Paul