first Reset your WAG102 to Firmware defaults.
configure your local computer to 192.168.0.36
then, install a tftp server (TFTPD32 http://jounin.net/)
place wagram_boot.img and wag102firmware.img into the root folder of this tftp server
now go to 192.168.0.232 using your webbrowser and login with admin / password 
use the firmware upgrade tab and use tftp_boot.img as firmware upgrade file
after the unit rebooted the real flashing procedure starts. this might take 2 - 3 minutes
but never break it while it still does flashing. this will result in a brick