Installing node on Debian Lenny is pretty straight forward. You’ll install the software required to build it, download the source, ./configure and then checkinstall.

sudo apt-get install python g++ make checkinstall
mkdir ~/src && cd $_
wget -N http://nodejs.org/dist/node-latest.tar.gz
tar xzvf node-latest.tar.gz && cd node-v*
./configure
checkinstall #(remove the "v" in front of the version number in the dialog)
sudo dpkg -i node_*

I haven’t used CheckInstall before, but it is a piece of software that automates the building and installing of packages.