The problem is that you need nvm to be automatically sourced upon login, so either add the following line to your ~/.bashrc or ~/.profile file.
[[ -s $HOME/.nvm/nvm.sh ]] && . $HOME/.nvm/nvm.sh
Also nvm doesn't set any version of node automatically so if you just installed nvm and installed a node version and try to use node the next time you login, you get an error that command not found: node unless you use the nvm use versionnumber command in every terminal session, so Instead I suggest you to set a default alias so that a default version of node is active for every terminal session using the following command
nvm alias default versionnumber
PS: In the above commands version number denotes the version number of nodejs that you have already installed using nvm
nvm install 0.8. – Eric Carvalho Mar 18 '13 at 23:21