If you want to mount samba shares with Greek filenames under Linux (Ubuntu, in particular), here's the magic command:
sudo mount -t smbfs //server/share dir -o username=guest,password=,iocharset=utf8,unicode
It took me a while to find, so here it is for posterity and for others who might need it. Ubuntu displays filenames correctly through the network without any configuration, but if you want to mount a share yourself, you need that. Same options go for fstab as well, it works the same way.