The local URLs must begin with a '/' char. This is a requirement of HSE_REQ_SEND_URL, which is used to send the file. When the HSE_REQ_SEND_URL is used, the user's current URL becomes something like "http://host.company.com/scripts/redir.dll?target=%2FPath%2Fto%2Ffile.htm". If you do not like this behaviour, you can use absolute URLs. This will force redir.dll to use HSE_REQ_SEND_REDIRECT_RESPONSE. This will cause the user's current URL to become something like "http://host.company.com/path/to/file.htm".
Running redir.dll either way causes additional data to be written to the web server's log file. The additional data appears in the parameters area and has the format "rdrRef=URL rdrTgt=URL". This gives you the ability to scan for these values in the log file and give credit to advertising pages. The rdrRef value is the HTTP_REFERER value if the client sent it and a dash '-' if the client did not send it. the rdrTgt value is the URL that redir.dll sent the client to.