PHP / cURL on Windows install: "The specified module could not be found."

I'm running PHP 5.2.3 on Windows 2000 Server with IIS 5. I'm trying to get cURL working, so in my php.ini file, I have this line:

extension_dir ="F:\PHP\ext"

And later, I have:

extension=php_curl.dll

The file F:\PHP\ext\php_curl.dll exists, but when I try to run any PHP script, I get this in the error log:

PHP Warning: PHP Startup: Unable to load dynamic library 'F:\PHP\ext \php_curl.dll' - The specified module could not be found. in Unknown on line 0