Using an External Hard Drive for media

I have the following:
I have an AppleTV in my Lounge (ATV1) - the drive is full so I am unable to download any other content from the iTunes store. This is sync’ed to my iTunes on my PC.
I have another AppleTV in my Bedroom (ATV2) - no content on it at present - I access iTunes on my PC from this Apple TV.
Both Apple TV’s have ATV Flash installed.
I have a Macbook Air - new and I am not very familiar with mac’s as I am a PC user
I have 2 x Time Capsule’s

What I want to do:
I want to use one of the Time Capsule’s (TC1)as the main source of media downloaded from iTunes instead if the hard drive on ATV1 and the use the second Time Capsule (TC2) as a back-up drive.
I want to be able to access all / any of my media on TC1 from either ATV1 and ATV2 and from my PC or any other media device.
I want iTunes on my PC to store media / look at the Timecapsule for media instead of the hard drive on my PC as it is filling up my hard drive on my PC.

Help! I would appreciate any assistance.