On the curl download page there’s a link to the download wizard. Complete all the steps as follows:
If you chose Windows / Win32 you should end up here, a page that links to http://www.paehl.com/open_source/?CURL_x.y.z (x.y.z will change as newer versions of curl are released). There you can click the first link (“Download WITHOUT SSL”) or second link (“Download WITH SUPPORT SSL”) for a zip file with curl.exe.
If you chose Win64 you should end up on this page which should have direct download links from the http://curl.haxx.se website. These too contain only curl.exe.
Finally, you can copy curl.exe into %windir% and it should become available on the command line.
** notes about final step.