I understand you're basically trying to digitalize your library and allow some streaming features to all your digital devices (mac, windows, tablet, phone, etc).
Now there are various options available to you, there are some factors to consider:
* How much data are you looking to store?
* How much time do you want to spend tinkering around with it (looking for a hobby or a solution)?
* Are you looking to stream this data outside of your home and if so, do you have the bandwidth to support the stream?
* How bad would it be to lose your data due to harddisk failure, or a fire?
With all points to consider, based on what you said my guess is that you would be okay to spend a little extra and have the "full solution" in place.
A "NAS" (network attached storage) device sounds like the thing you need here, you can build those yourself, but is rarely much cheaper then grabbing a NAS device from a manufacturer (we're talking maybe 10~50 dollars you'd save here, not counting the hours you'd have to invest to get the software running). A NAS generally is a suite of different solutions and connection methods allowing you to make your storage widely available throughout your home.
Most come prepacked with nice proprietary software packages that offer you all the features right out of the box!
My personal favorite brand on NAS devices is Synology, relatively new but make very nice devices which they frequently update, even on older models.
I have a DS212j at home, with 2 x Western Digital Red 2TB disks in it running in a redundant RAID-1 setting.
Offering a wide selection of connection methods I managed to hook this device up to my PC, media center running XBMC, TV, Home cinema system, laptops and tablet.
Its icing on the cake is its webbased management interface which looks like a windows environment on it's own, very easy with all kinds of navigation windows, external software packages you can click&install and separate interface when using mobile devices or tablets. I can for example now stream my library using the integrated audio-player at work without even having to install any software there. there is also a download tool integrated, All in all it is a lot more then i'd get with a software package as FreeNas for example.
Some are suggesting a XBMC setup which is more of a media-center solution, not as much a storage solution.
I prefer to keep those separate as playing entertainment media and storing data are 2 different purposes each with their own requirements.
I hope this helped you with your choice!
PS. when getting disks, you'd want to go for the more durable series, desktop drives aren't really made for NAS devices and might give issues, my 2 cents, stick with western digital REDs, which are specially made for NAS devices, both cheap and pretty durable.