Paul... is the script i am trying to use really that bad?
The lists are wrongly constructed in that the sublists should be within the <li> tag and not outside it. Also an id should be unique to the page but its been used more than once in their example.
If you don't care about these things then use it. Doing what I suggested above should stop dw re-writing the code. Otherwise turn off code re-writing for that page like junjun suggested.
Alternatively look at those 2 links I gave you which come highly recommended by zeldman and a list apart.
Just checked your link with dw editing the code and the menu seems to work ok!