1) Create a directory off the webroot, ex, "protected".
2) Inside that directory, create an .htaccess file, eg:

AuthType Basic
AuthName "Restricted content"
require valid-user
AuthUserFile "/home/user/.htpasswds/public_html/passwd"

3) Create a directory the same as the node you're wanting to protect (eg, /webroot/node/10) and put the above file into it (this will break Drupal if anyone tries to go there directly, so they won't be able to see anything)
4) Create an alias in Drupal (configuration, URL aliases). Make the alias /protected/login (so it's one level down on the directory you created in step 1)

Now when you go to domain.com/protected/login, you'll be prompted for credentials. /node/10 will no longer be accessible.

Grant Lawsky
gnlawsky@gmail.com