Smooth lines in foil

[Matthiasb]

Is it possible to make something like here (http://www.de-website.net/tijdelijk/eg.jpg) (below in the window) in Illustrator and how do I make that?
Thanks for the help.

Update: I tried this (http://www.ehow.com/how_16666_make-wavy-zigzag.html) tutorial but I think that's not an ideal way to do this... I'd like to choose where the "waves" are and how big they are.
I think the most difficult (for me :) ) is to make the line "smaller" and "fatter" at some places...

[Husker]

There are a lot of different ways you could do this but this is the way I did it:

http://vectorgeek.com/artwork/images/Wavy-subtract.jpg

[Husker]

I should note if you want to vary the thickness you can use an art brush and expand the brush to use it to subtract from the underlying shape or just manually tweak the paths in this version.