install the php libcurl extension (sudo apt-get install php5-curl on ubuntu).
But I keep wondering why I need curl.
I see curl as a security risk - I don’t want users to use my server to browse the world ...
Why would I want to grab an http/ftp or whatever source from another server?
On my site I do not want to use any of the carrier modules, I don’t even want any users on my server to be able to use curl.
so I am missing why curl is a requirement for Magento - one should be able to install a system without it.