The only thing that worked for me on Elementary OS Luna, a Ubuntu Fork. I am on x86 architecture. I tried all the answers here but finally decided to install it from source.
First, make sure its not installed using the package manager:
sudo apt-get purge nodejs npm -y
I went to the download page to lookup the latest source & download it, http://nodejs.org/download/. You can use curl, wget or your browser to get it:
wget http://nodejs.org/dist/v0.10.34/node-v0.10.34.tar.gz
tar -xvf node-v0.10.34.tar.gz
cd node-v0.10.34
./configure
make
sudo make install
The make might take a while. When done, you should have node and npm installed and working in your /usr/local/bin directory which should be already on your path. You should verify where it lives:
which npm node
I also had to change the permissions to get it to work:
sudo chown -R $USER /usr/local
If it didn't work check your path:
echo $PATH
Note that installing it this way, it will not be managed by apt-get package manager. Cheers!