danielson,
simply download and install curl itself, during your php configure, add the line:
--with-curl=/path/to/curl
Generally the path is not necessary if curl is installed in default location.
Note: be sure curl is compiled with SSL support if you plan to use that, check it's install logs to save some hassle later on.
hope this helps.
-m.
cURL: http://curl.haxx.se/