After some experimenting I found out the following:
Stop the firewall -> I could use the samba share
Start the firewall -> Samba shares could not be used anymore
In advanced settings (or edit it straight in /etc/sysconfig/SuSEfirewalll2) open all ports:
FW_SERVICES_EXT_TCP = 1:2048
FW_SERVICES_EXT_UDP = 1:2048
and start the firewall:
# SuSEfirewalll2 start
Again I cannot use samba
According to the help of the firewall it should be possible to see (in /var/log/messages) what is blocked when using the test mode. The firewall will not block anything but log in the logfile what would have been blocked by the filterrules. So let's try:
# SuSEfirewalll2 test
I tried to open the samba shares on my machine and ...
nothing in the log file and again I could not reach the share.
# SuSEfirewalll2 stop
and ... I could use the share! So the firewall was blocking something after all although it should not have according to the help file!
A small note: I tried to use the shares from a Windows 98 machine and rebooted the machine between every step of my experiments.
I give up.
Since I am behind a hardware firewall I do not care much about this one and decided not using it until someone finds a solution to this problem.