Hi Anniebel.

What David says is correct. Especially the bit about the diffuse colour. A diffuse colour of 100% white will totally wash out any reflections. Depending on how much reflection you want from the dress, reduce the diffuse value (0 = black, 1 = white, other values inbetween), or  change the colour (you could, for example, change the colour to a very dark red.. try it and see what difference it makes..)

But pure white just won't work...

Cheers,
Diolma