CURL problem

Just installed Drupal 5 on my Windows XP system and added the amazontools module in. When trying to submit an Amazon node, I get

warning: DOMDocument::loadXML() [function.DOMDocument-loadXML]: Empty string supplied as input in C:\Websites\drupal-5.0\modules\amazontools\amazon.php5.inc on line 328.

Tracing amazon_get_XML(), $url contains a valid URL (pasting it into Firefox gives me the appropriate XML). There are no errors from CURL, and curl_init() seems to return a valid resource ID. But, nothing comes back from ob_get_clean().

From phpinfo():

PHP Version 5.2.0
PHP API 20041225
PHP Extension 20060613
Zend Extension 220060519

curl
cURL support enabled
cURL Information libcurl/7.14.0 OpenSSL/0.9.8d zlib/1.2.3

dom
DOM/XML enabled
DOM/XML API Version 20031129
libxml Version 2.6.26
HTML Support enabled
XPath Support enabled
XPointer Support enabled
Schema Support enabled
RelaxNG Support enabled

Any thoughts?