Very Easy to do.
If ure running Apache on Windows, u need to edit the http.conf to contain these:
LoadModule php4_module c:/Website/php/sapi/php4apache.dll
&
AddModule mod_php4.c
in the sections with the other LoadModule and AddModule entries.
you'll also need:
AddType application/x-httpd-php .php .php3 .phtml
somewhere in there.
obviously with the path to that file, it is included with the FULL PHP distro, not the small one.