I tried opening the registry in Win7, but there seemed no way to
specifically target a new folder within "Documents". The registry
just wants to use "Documents" under the relevant user name.
The registry wants nothing. It's a database.
You have to enter the data (folder name) you want, as described in the
article you were directed to. You do it by typing it.
You need to proofread about three times before exiting, however. Or at
least I do. Although in a way it doesn't matter, since the change is
made as soon as you type and accept it.