There is another thread running about these here:
Lastollite Hilite Backgrounds
Mark Cleghorn who has made a lot of posts is very well known in the UK for his lighting techniques and seminars, so if its good enough for him ...........
However, being one to always plough my own furrow, these were taken last weekend:
Gallery 5628 Background is a white cotton sheet 9' wide and backlit with a single 36" umbrella set to overexpose the background to burn the creases out.