The Canon Scanners w/OS X Leopard (notes on support, alternative (Twain SANE) drivers) page was updated again this morning with notes on a G5 tower/Epson 2400 (and 3170, 4870) owner on using the (pre-10.5) twain driver in Photoshop OK and noted using the (older) v2.65A Epson Scan software (stand-alone) OK as well. (He never updated to 2.77A.)
Also added two more 2450 scanner user reports - one OK, the other not (the latter mentioned the scan utility version is listed as 2.73 although the download at Epson's site lists 2.77A)