Any decent NAS "box" should be able to do what you provide. The Windows Home Server (2011) suggestion is also a good one but I don't have any on hand experience of this.
To give you a quick idea my "home server" setup is a Buffalo Linkstation Duo hooked up to a *temporary* Philips router incorporating a 4 port Fast Ethernet Switch.
My Laptop and desktop can then connect wirelessly or via Ethernet and stream video / music or access files as if it was another folder on the computer. My PS3 can also see the NAS as a DLNA compliant media server and can act as a DLNA compliant media player (as long as your videos are encoded in a "readable" format).
As a basic setup using a NAS you would have something like this:
NAS - holding your media / files which you wish to share > Mirrored backup of important files (either schedule or Ad Hoc)
Wireless router w/ switch or seperate switch (there are many options here - choose which is best for your setup)
Latop connecting wirelessly
Desktop connecting via homeplugs / Ethernet
Any other DLNA/uPNP compliant device connecting either wirelessly or via ethernet.
Whether your devices connect wirelessly or via ethernet will be up to your specific setup / requirements. Ethernet will be much faster (especially if it is Gigabit) but wireless N should suffice for normal media streaming (Non HD).
A Windows home server would work in a very similar way to the NAS box but can be more flexible depending on your usage requirements. It can be more difficult to setup but there are plenty of guides / youtube videos out there to help you should you get stuck.
this i just got strike that NAS can be a DLNA server...great , i am going to setup one so that everyone can hook up and listen to it..