Logger and RAILS_ROOT

Hi everybody,
I’ve juste installed Ruby on Rails on Windows with Instants Rails.
I’ve made a small web app which work fine but…
I cannot log : I tried logger.info but no result in development.log.

So I read the doc and then created a file named debug.log in the same
directory than development.log.
But when I start Webrick, the console write a message : "Unable to
access log file: Please ensure that log/debug.log…

I understood that the path is set by RAILS_ROOT. But where can I set

If anyone can help, it will be easier for me to write code with a