I had some problems installing the libv8 gem after installing ruby 2.0. The solution was to use yum to install the python26 packages and then make a link from them to /usr/local/bin/python. After that the gem install libv8 command worked.

$ yum install python26
$ ln -s /usr/bin/python26 /usr/local/bin/python
$ gem install libv8

This worked on both an RHEL6 and an RHEL5 system. I needed libv8 because therubyracer gem depended on it.