Two problems. First, the CGI process is probably being run as a user other than you. For IIS, there is a special user that gets created just for this purpose. That user most likely has no access to the particular directory that you want to map.

Second, even if you give the web user access (read-only access, I'd hope -- otherwise a rather risky proposition) or change which user the web server runs CGIs as (also a rather risky proposition), some web servers will run CGIs in a security context that does not allow access to any "Windows networking" resources (no matter what user they are).

                - tye