be sure to edit your php.ini file:
doc_root="c:\web" (changed c:\web to whatever your webservers root directory is)
extension_dir="c:\php" (change c:\php to whatever your php folder is)
Be sure to copy your php4ts.dll file to c:\windows or c:\winnt
then in your apache.conf
ScriptAlias /php/ "c:/php/"
AddType application/x-httpd-php .php
AddType application/x-httpd-php .php3
AddType application/x-httpd-php .php4
AddType application/x-httpd-php .htm
AddType application/x-httpd-php .html
AddType application/x-httpd-php .phtml
Action application/x-httpd-php "/php/php.exe"
be sure to restart your apache server after that