How to disguise your PHP script as a browser?
Try escaping your URL, it works for me that way.
http://mediaforest.ro/weeklycharts/viewchart.aspx?r=WeeklyChartRadioLocal&y=2010&w=46%2008-11-10%2014-11-10
Use curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12');
You can replace the useragent with another one of course.
However, "Bad Request" is most likely NOT related to a missing/bad useragent. It sounds like the webserver itself doesn't like your request.. not the application behind the requested URI.
I had to lose 'Accept-Encoding: gzip,deflate', from the $header to get it to work properly on my godaddy website.