Clearly you can connect an external USB hard drive and access the content using the XBOX. However, I'm unaware of any means to make that same content available OUTSIDE the XBOX, specifically, as a NAS. That would require the XBOX provide a server for those purposes (http, ftp, whatever). And I just don't see why MS would do that. What's in it for them? If anything, it would now compete w/ their own server products.
FWIW, I did find the following tutorial over at SmallNetBuilder which shows how to make a NAS out of an XBOX, suggesting that it has no such inherent capabilities. Notice that it essentially guts the XBOX for the purposes of a NAS (probably not what you're looking for).
Granted, it's a very old article referring to the original XBOX, but I doubt the situation has changed since then. But who knows, maybe someone else knows more than I when it comes to XBOX. I’m not a gamer, so hardly an expert.
i have scoured the net for a way of doing this to no avail and therefore agree with you it is obviously not possible to use as a media streamer.
oh well homebuilt nas it is then.
thx for your promt reply eibgrad