there are lots of ways to do it i do it by using a image of a crumpled paper that i either scanned or photographed you can also get images online of this texture at sites like the stock xchng
www.sxc.hu
put the crumple over the the paper you want to crumple and set the layer style to multiply adjust the opacity or the brightness and contrast to get it perfect.
you can also use a filter like xenofex some programs come with this texture in it already like DIP
HTH
Tanya