install wordpressmu+buddypress locally using mamp

I've tried to install wordpressmu+buddypress locally on may mac...
I saw a step-by-step video... actually is quite easy, but in the end i couldn't change my hosts file...
I downloaded mamp, installed, changed the preferences (like the video says)
Installed wordpressmu and buddypress in my sites folder
I did all the processes from the video, but at the end my hosts file didn't appear like the file in the video...
When I type mate etc/hosts in Terminal, TextMate opens the file but the file is empty... I couldn't change to localhost.domain
Does anyone can help me?

 

actually the slash is in the video... my mistake! stupid girl!
thanks
it works great!
I edited the file and my wordpressmu works great!