Thanks to all that offered help with my SxWiki problem. It was indeed the User Agent. I was able to get around it by adding this line to the _curlDo() function:
curl_setopt($ch, CURLOPT_USERAGENT, 'JaGaBot (using SxWiki 0.1.0)');
... just in case some other unfortunate soul runs into this problem.
Thanks again!
- Jason