I am assuming you have a 3CP260.60-1 CPU, where you have to go on-line through RS-232. Going on-line with rs-232 within AS2.7 can, indeed, be a bit fiddly.
Now I have never worked with System 2005 myself, but we have projects with the 2003 CPU's and can only be accessed through RS-232. To correctly configure an RS-232 connection in AS2.7 you have to go to Tools->Options. Under the Online tab choose a configuration that is configured for RS-232, or add a new one. Once done, click on Properties. In the new window select the correct serial port under Interface. Baudrate should be 57600, parity even and timeout 1(These are the standard settings).
AS2.7 will only begin to search for a PLC once you pressed OK on both windows(Properties and Options)
In the left-lower-right corner you'll see when it has connected. Once connected, you can download the program to the PLC.
You can not retrieve an existing program from B&R PLC's, because they only upload binary/compiled files onto the PLC's and not token files like with Omron, which can be loaded back into the IDE. Also, be aware that when you compare PLC programs in a B&R PLC, only the timestamp is checked. The programs are not actually compared.