Documenter.zip should be extracted to a folder of your choosing. 
It could be placed with the other add-ins at:
C:\WINDOWS\Application Data\Microsoft\AddIns\

If you choose to place it in the XLSTART folder, the add-in will 
automatically start, but it will not automatically open a blank 
worksheet. This special folder is usually located 
at: 
C:\Documents and Settings\UserName\Application Data\Microsoft\Excel\XLSTART .

All the files should be located in the same folder.

Using Excel's menu click Tools, Add-ins 
and then press the Browse button. 
Select the folder that you just choose click, Open Documenter.xla 
and click the OK button. The add-in will then become functional.

Click the Tools, Documenter menu or
click Ctrl+q.