Locate your PHP extensions directory. It should be defined in your php.ini file via the extension_dir setting (usually "c:/<some_path>/php/ext"). Open that folder in whatever tool you like to use to view directories, and see if it has a file called php_curl.dll in it. If it does, then all you probably have to do is uncomment the line in your php.ini file (or add it if it does not exist):
extension=php_curl.dll
Then just restart the web server and you should be good to go.
If that does not do it, then we'll have to look further into it, but hopefully that's all you need.