1.7.0 Update Collection Could Not Open http:/www.joomla.org/update/core/list.xml
From Joomla! Documentation
The Joomla Updater uses the php fopen command.
Those php configurations without fopen enabled will error with the following messages:
Update: :Collection: Could not update http://www.joomla.org/update/core/list.xml
Update: :Collection: Could not update http://www.joomla.org/update/jed/list.xml
You will not be able to use the Updater without enabling fopen for PHP. This is a web hosting issue.