DIY people: Shelving in the loft

[DEL 707]

I've got quite a few DVD/old games in my loft at the moment, a good few boxes. I'd like to put up some sort of shelving up there so they're on display, but there isn't much in the way of room. So I was thinking of putting up shelves inbetween the supporting beams.
Whether this is a good idea, or safe, I don't know .

Here's a very crude drawing. Will try to get a picture when I find my lead.

There's a length of wood that connects all the beams together along their back.
So the big question is, am I going to be casing any damage but attempting to put up some crude shelving?

 

[DEL 707]

Wait, so you want to put them on display in your loft? I assume the loft has been comverted into a room?

No no, I'm not converted it. I'm just out of room to store old films/games, which is why they're all boxed up, I would like a shelving system, so that if I fancy digging out an old film, I don't have to go rummaging through boxes.
This will not high class stuff, my DIY skills are basic, bordering on dangerous.