The default username:password on the APC card is
You can configure it through the UPS it's installed in via the proper APC (black) serial cable. Please don't use a generic 9-pin cable. You'll need to connect using a terminal emulation program (minicom, cKermit, Hyperterminal, screen, etc.). The key to doing this is stopping powerchute (or any UPS control software on the server connected to the UPS), setting the BAUD rate to 2400 instead of 9600, and pressing the reset button on the interface card. You should be able to navigate the resulting text menus to gain IP information and reconfigure user names/passwords.
From the documentation for the AP9617 card,
5. Press the Reset button. The Status LED will flash
alternately orange and green. Press the Reset button a
second time immediately while the LED is flashing to
reset the user name and password to their defaults
6. Press ENTER as many times as necessary to redisplay the
User Name prompt, then use the default, apc, for the
user name and password. (If you take longer than 30
seconds to log on after the User Name prompt is
redisplayed, you must repeat step 5 and log on again.