Essentially, you separate the diffusion from the light. So you need a frame of some kind. Imagine a shower curtain rod but much longer, suspended 10ft in the air. You hand a sheet of diffusion from it. Then stand the light off behind it far enough to cover the entire piece of fabric. Now your light source is as large as the fabric. There are a few caveats to this.

1. The denser the fabric, the more light you lose
2. The further the light from the fabric, the less light you'll have on the subject.
3. Potential for spill exists if you don't take care.

So typically, the "silks" or diffusion is on a square frame. The diffusion has grommets in it at regular intervals. And you suspend the diffusion in the middle of the frame (say a 9x9 piece of diffusion in a 10x10 frame, using cord which keeps it centered. That frame is usually held by a pair of c-stands or larger stands for bigger frames.

Really, it just comes down to what you want to light. You could do this as simply as heading to your local hardware store and making up some frames in 1" pvc. That's what I did. It's light, it breaks down well, and it's cheap. If you want an 8x8 frame, buy shorter pieces plus corners, and some couplers. That way you can break each side down into 2 pieces instead of having 4 8ft pieces, you have 8 4ft pieces.

Some fabric, a grommet kit, and some shock-cord, and you're in business. The tricky bit is finding a way to keep the frame still! Of course the professional applications have "fingers that fit into a c-stand arm. Maybe one day when I have money!

Oh, and don't blame me, blame AC Magazine. The more I read that thing, the more harebrained ideas I get. This month's is PARTICULARLY bad with the Bengamin Button review and showing the setups for Revolutionary Road. Great issue if you can go pick it up.