well, as I told you before, use a a text editor with a replace tool,you can use for example edit plus ( it runs in windows)

for example, your passwd:

smith:*:100:100:8A-74(office):/home/smith:/usr/bin/sh
guest:*:200:0::/home/guest:/usr/bin/sh
...
....
.....

in the replace command you can put something like:

*:/home replace by mkdir /home

then your replace
:/usr/bin/sh for a blank space

and thats it, you have your script.. you dont have to do any thnig else!!
Hope you get it, if not it would be easy that you email your passwd and then I return your script.