Any suggestions on how to use the open(); command when trying to access a location that requries credentials (username & password)?
Jim's suggestion is also good (and maybe simpler). Here's an older post on FTP.
In the Scripting Reference Book, there is a good deal of information on the options available to the Open function. Password is one of them, however, I don't believe it will help you in gaining access to a server that you need a userID and Password for. What I have done in the past, is to use FTP. You can create a file with the FTP instructions that you need to down load your file in question, save it, and then execute the FTP command, using the "Run Program" function, with the option pointing to the file. Then open the down loaded file.
try this , uses curl via runProgram.