Ok, what I would suggest now is to remove the mod_rewrite bits so that all your .htaccess file is doing is serving to change the type of php in use. The create a file called info.php in your root and write a script that just contains the phpinfo(); command echoed, and enclosed in the appropriate php tags.
Unfortunately that is exactly what i was trying - i have a .htaccess containing just the php code, and a test php file with just phpinfo(); in it. If I remove the .htaccess file and refresh it shows the php4 info fine.