You cannot take advantage of the $50 credit for the Connect store without it. That said, you could use
Libprs500 to talk to your Sony Reader. But before you install it, make sure the USB driver for the Sony Reader that your copy of Connect may or may not have installed is not still installed. Once you are sure that is gone, you should be all set.
Do you happen to run a 64-bit XP? If so, Connect will NOT work. THe other thing I am thinking is because the Reader is a US only product (at the moment) that Connect just simply doesn't work with other then an English XP/Vista.