NPM is made successfully and can be run via ./cli.js but there is no alias made for npm. Running under Snow Leopard.
In the node repl, what do you see when you type this?
Did you install node with Homebrew? If so, it is a bug in homebrew, and npm ends up installed in the node Cellar folder.
If you pull homebrew from here, and then uninstall and reinstall node, it should work: http://github.com/reid/homebrew
More info: http://github.com/mxcl/homebrew/issues/issue/1552