How do I add users to my WP blog with VERY specific access only?

Hi, my question is very specific. I need to be able to add users to my wp site.
These users will only have access to 1 area of my wp site which is the 'add locations' tab of my store locator plugin and nothing else.
How can I achieve this?
(Also, are you planning a store locator plugin? Or how can I request one? Thanks ; )