I could setup multiseat on F17 just by deleting some udev file which are automatically generated. and using logintech command to nominate some hardware to a special seat. and finally writing a myudev rule. the syastem works great but on a reboot I get all things messy. so I have to go to init 3 and log in as root an execute GDM START. in this way both seats work well. after updating linux kernel it happens seldom.