I'd try to install a new printer from scratch with the OS X onboard program Print Center (located at Macintosh HD>Applications>Utilities). Connect the printer to the iMac and turn on both. Click the "Add new..." button (instructions from OS X 10.2, it may be slightly different in 10.3) In the popdown menu, select "EPSON USB". Your printer should then appear on the list. Acknowledge the printer and finish the installation.
Check if your printer is selected in the print dialogue if you print from AppleWorks or MS Office.
Since Epson claims support for OS X 10.2 and later, you could also have a shot at the CDs if there came any with the printer (you probably need them anyway for scanning).