When I record a 2.5 hour movie to MPG format on my TV tuner it takes up about 5GB of space. I Have found that my 500GB hdd is loosing space very quickly.
If you manage to get them compressed onto MPG format and fit under 5gb of space
2 500GB HDD is not unreasonable in your case. Also I would not recommend streaming video wireless unless you got a wireless N connection.
So if you manage to get them compressed onto a MPG using a on card TVtuner compression then you could do it with 2 500GB HDD or a Terabyte Hard Drive.
I would not recommend Windows Midea Center Edition becouse then what pip22 Says about 13GB is completely correct.
What I use for my PVR/Media Server/File Server is MythDora Plus Best of all it is free.
Here are some instructions on how to install it. Here is where you get itIf you want to Get a Tv tuner to add to it I would recommend Getting a Hampague TV Tuner. They seam to work the best and in addition to that they encode on the card so it takes up Less CPU.
I would also invest in a good IR computer Remote one of the sides above did a review on one that I am planning on getting.
Also for redundancy might want to think about Doing a at Least A Raid 1.
Don't ask me how to do it yet that is my next project is setting up a Raid. Might want to go to the Hardware Forum for more info on that.