[Boofo]

Here is what I use and it works fine for me.

# Hotlink Protection - images
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(.+\.)?yoursite\.com/ [NC]
RewriteRule .*\.(jpe?g|gif|bmp|png|mp3|pdf|psd)$ /forums/images/nohotlinking.jpg [L]

# Hotlink Protection - attachments
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(.+\.)?yoursite\.com/ [NC]
RewriteRule .*attachment\.php*$ http://www.yoursite.com/forums/images/nohotlinking.jpg [L,R,NC]