Instant file sharing between users in PHP

Working on a rather complex system in which users can directly exchange files with eachother from the website. However is any of these things possible:

EITHER

* Have another user download a file which is still being uploaded by another user ( in progress )

OR

* Make a user automaticly ( instant ) download a file from another users PC through our website

OR

* Make a user automaticly (instant) download a file from our server ( so it's directly downloaded to the users pc and the progress shown on our website of the download progress, without the normal internet explorer dialog downloading the file or firefox ).

Thank you very much in advanced,

Best Regards, Webcodez.net.

UPDATE: an example would be MSN's file sharing but then through a website in开发者_如何学Cstead of application.

Bad news - there is a reason MSN does that in an application. Given users are likely t obe behind NAT (i.e. their computers not reachable) and tha tyou dont want a website abusing your computer to send spam (i.e. open random network connections) websites are LIMITED.

So, you have a nice wish, it is not possible and I am REALLY happy it is not possible. Being a user and so.