B&R, like most advanced controllers, uses compiled code on the PLC and you must do an extra step to transfer the source code to the PLC. In AS3.X and 4.X, B&R made it very easy to transfer the source code to the PLC, but in earlier versions it was a more manual process.
System 2005, despite the name, was released in the year 2000 and so is now getting pretty old. your system was probably originally programmed in AS2.X and so it is unlikely that the PLC has the source code downloaded to it. You will need to track down the people that originally made the machine to get the program from them. You might get lucky though, you can connect to the PLC using an FTP client and check the F:\ partition to see if the source code was placed there.
I don't know about the 2005 product lines, but you usually program a B&R controller with a regular ethernet cable. If not, you will probably need a standard serial cable with a null modem and a gender changer (so the cable has a female plug on both ends and swaps the Tx and Rx lines). You can make your own if you have two female, 9 pin D-sub connectors, there is nothing special about it.