Content area on external server

[okc]

I would like paid subscribers to be able to DL large attachments (say a 400mb video, for example) from my server, but I want that content to come off a server/location external to my vB server. I assume the attachment might be a link to a location on the external server, but

(a) Is this the right method to make sure the media files don't slow down/impact the bulletin board

&

(b) How can I protect paid subs from sending the link address to their friends

thx