I have LAMP installed on my linux distribution:
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PHP 5.4.9-4ubuntu2.4 (cli) (built: Dec 12 2013 04:29:20) Copyright (c) 1997-2012 The PHP Group Zend Engi
As Michael Berkowski says, the 2.x branch is totally new and it works with a different API.
You can go with the 1.x branch and use the old functions this way:
pecl uninstal pecl_http
pecl install pecl_http-1.7.6
Then you can use http_get
Anyway, if this is a fresh new project, it is recommended to go with the newest API.