Finally I got my Epson Perfection 3490 Photo scanner working on Ubuntu 9.04 (64bit). It was much easier than most forums wanted to make me believe and it did not require hazzling with "*.rpm to *.deb conversion" or installing non-free software (except the Epson firmware file for the scanner).
Here the way I went:
1.) The following packages were already installed on my system (I don't know, whether one or more of them are not required, but with all of them installed, it works): libsane, sane-utils, libsane-extras, xsane, xsane-common
2.) Get the firmware file "Esfw52.bin" for the scanner, which can be found in the cab-archive "ESCAN/LIB/ModUsd.cab" on the original Epson Scanner Software CD-Rom (delivered with the scanner). In order to retrieve the *.bin from the *.cab file, copy this *.cab to the hard-disk (lets say to the temporary folder "~/Scanner" for example), install the package "cabextract" and then run in a terminal
After this you should find "Esfw52.bin" among several other files in "~/Scanner".
3.) Now copy this firmware file to an appropriate place in the file-system by typing
sudo mkdir /usr/share/sane/snapscan
sudo cp ~/Scanner/Esfw52.bin /usr/share/sane/snapscan/
in a terminal.
4.) To tell XSane about this new firmware file, just change the line "firmware /usr/share/sane/snapscan/your-firmwarefile.bin" of the file "/etc/sane.d/snapscan.conf" in "firmware /usr/share/sane/snapscan/Esfw52.bin" by entering
sudo gedit /etc/sane.d/snapscan.conf
in a terminal (don't forget to save your changes in gedit).
5.) Now connect your scanner to the computers usb-port and to a power-socket and start XSane from the application menu. XSane will show a welcome-screen that asks you to select your scanner in case the system detects more than on capturing device on your computer (like other scanners, webcams, etc.).
6.) Since it is now not more required, you can delete the temporary folder "~/Scanner" with the *.cab and *.bin files by typing
rm -r ~/Scanner
in a terminal.
And that's all. I hope, it was not a lucky accident, that it worked on my system. If you have comments or remarks, please answer to this posting.