Midgard-php4 is a regular extension to PHP4. You can compile it either as part of PHP4 itself, or as an self-contained extension.
To compile it as part of PHP4, copy the directory into the ext tree, run buildconf, then configure using the --with-midgard switch. All normal rules to building PHP itself and any other extension apply.
To compile it as a self-contained extension, run the mkall script in the midgard-php4 directory, then add a line like
extension=midgard.so |
to your php.ini