And yes it is possible to install node on windows 7, in fact.... Its really really easy actually.
1. download node.exe from http://nodejs.org/dist/v0.6.0/node.exe (link avaliable from http://nodejs.org)
2. create a sample node app
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello World\n');
}).listen(1337, "127.0.0.1");
console.log('Server running at http://127.0.0.1:1337/');
save in a file 'example.js' and place in the same folder as node.exe (anywhere on your system)
open a command prompt in the folder with node.exe and your .js file
run >
node example.js
and thats it, now open your browser and goto: http://127.0.0.1:1337/
Hello World
how easy was that?