I had a problem setting up an Epson USB printer using CUPS - It turns out that whatever version of cups I had had a problem with detecting USB printers.
Try pluging in and switching on your printer, and then restart the CUPS daemon. The easiest way to do this may be to reboot your computer... Then try setting it up again.
*edit: This worked for me, but it may not help you
Also, use the web-browser interface for setting up CUPS, http://localhost:631
I hope this helps