...well, first set permissions on the 'googlecheckout' folder to 777

- Then go to the admin section of ZenCart, Modules>Payment, and select googlecheckout and click edit

- select 'True' under .htaccess Basic Authentication Mode

- under '.htaccess Basic Authentication Mode' click the 'here' link where it says "If setted True you MUST configure your .htaccess files here"

- on the .htaccess .htpasswd create window enter your checkout account, sandbox account or both. Put a check on both the 'Check if dir exists' and 'Create Files' checkboxes. Click 'Create' and close that window once it's finished.

- Now click 'update' on the googlecheckout settings.

- Change permissions back 755 on the 'googlecheckout' folder.