Options for home data storage and access from multiple PC's

Hi,
I am putting together a new gaming PC and will put together a HTPC that can record TV in a few months time. I am considering options of how to store the data, photos, music, video's etc, so I can look at it from both my gaming PC in study and HTPC on the TV (ethernet), maybe even my laptop (wireless). I want to be able to back up the data as well. Will be putting in gigabit network and cables etc through the house.

My thoughts are:
1. put a few HDD's in gaming tower and let HTPC access this drive. Set up either a raid or just back up to 2nd disk every week.
2. put a HDD in HTPC, keep live copy of info there and back up to gaming PC every week.
3. NAS?
4. Revitalise my very old AMD athalon 64 to act as a server - probably very slow
5. some sort of cloud backup option?

Currently I don't have much data, but with a young child, lots of photos and video's get taken, and being able to record TV will increase data storage requirements pretty quick!

Also, what are thoughts on best HDD's to use?

Thanks, Oxidised