Rather than a file which won't really explain anything...
http://www.freefind.com/library/howto/robots/
... some explanations to go along with it.
The default robots.txt that ships with Joomla 1.5 looks like this:
Code:
User-agent: *
Disallow: /administrator/
Disallow: /cache/
Disallow: /components/
Disallow: /images/
Disallow: /includes/
Disallow: /installation/
Disallow: /language/
Disallow: /libraries/
Disallow: /media/
Disallow: /modules/
Disallow: /plugins/
Disallow: /templates/
Disallow: /tmp/
Disallow: /xmlrpc/
HTH