Use TWAIN SANE -
http://www.ellert.se/twain-sane/
1. Basically, install all the snow leopard binaries from the web site above, except the SDKs.
2. Download the XP driver of Epson Perfection 660, unzip it. You will find a firmware file under DATA called TAIL_061.BIN
3. Point the driver to that firmware by going to System preference -> SANE. Configure the driver called "snapscan". The top of that config file should be like this (note that I put the firmware file in /usr/local/share/sane/snapscan/):-
#------------------------------ General -----------------------------------
# Change to the fully qualified filename of your firmware file, if
# firmware upload is needed by the scanner
firmware /usr/local/share/sane/snapscan/TAIL_061.BIN
# If not automatically found you may manually specify a device name.
# For USB scanners also specify bus=usb, e.g.
# /dev/usb/scanner0 bus=usb
# For SCSI scanners specify the generic device, e.g. /dev/sg0 on Linux.
# /dev/sg0
#---------------------------------------------------------------------------
There you are. It works with my Macbook Pro 13" with OSX 10.6.4