Is it possible on a raq3 server to disallow certain file types from being viewable or downloadable via the net on a specific virtual site?

what about limiting the max file size on a specific virtual site ?

if so how ?

i.e.

if i don't want a virtual site to upload a 6MB *.rm *.mov *.zip *.tar *.mpg *.mp3 file and offer it for download on their site. How would i set that up on a per virtual site basis ?

or if they upload a file like that.. make it so that it can not be served to the net via the browser etc ?

how do hosts police such stuff ?