If you don't want to pay the M$ tax with WHS, here is a great alternative. Full disclosure: I am part of the core team of this Open Source Project, so of course I'm biased
. I have used Amahi for 2+ years. And did I mention, It's Free!
http://amahi.org The Amahi Home Server is based on Fedora 12 , but don't let that scare you off if you are not a linux user. Amahi comes with most things preconfigured (like shares for Music, Movies, etc), so you don't have to mess with all those config files (unless you want to). Hardware requirements are reasonable, I run mine on an Atom 330 with 2GB RAM and 1TB HDD. Amahi has one of the largest App stores of its kind, with all types of Open Source software packaged for One click Install. I'll list just a few that are in your requirements:
CrashPlan for backing up all PC's on your network.
Coming soon: Redo Backup and Clonezilla for bare metal backups.
Amahitunes: an iTunes server based on the Firefly Media Server
Jinzora another media server
Squeezbox Server
OpenVPN: preconfigured out of the box, also an easy to use Windows client.
Transmission One click install for torrenting, web based interface
Torrentflux B4rt Another web based Torrent software
Edit: forgot to mention DLNA
DLNA Server based on miniDLNA so you can stream media to XBox and other devices
I'm not much of an iTunes fan, so I just point Foobar 2000 on my Windows machine to the Share where my Flac's are and stream away right over the network.
I do the same with Movies, via XBMC on my HTPC.
For more info check out the site. There is also an IRC channel on Freenode #amahi, or
http://talk.amahi.orgAlso feel free to PM me with any questions.
Good luck,
Pat