Under Page Setup, and under the bottom dropdown menu, you'll choose Manage Custom Sizes. When in the resulting dialog box, click the + button to add a new paper size. Double click on the name, which defaults to Untitled to rename it, and then plug in the horizontal and vertical dimensions. You will have to then go back and choose that new paper size before going on to Print w/ Preview.
Hi - I am also trying to print out panoramas of a similar size (40" x 16") - I have read the string with interest but dont seem to have the same dialogue boxes as you mentiion.
My set up is mac osx 10.3.9 + photoshop cs version 8 + epson 4800 connected via firewire, I am using 17" roll media (none epson) which has been profiled using monaco profiler software.
You state 'Under Page Setup, and under the bottom dropdown menu, you'll choose Manage Custom Sizes' - I do not appear to have this option... is this from ps or epson print interface?
Obviously I have the ability to create a custom page size with 3mm all round but again don't have the + button bit.
Hope this all makes sense