Okay - I solved the problem last night
Here is the short version of what I did (and I verified it on a second OpenSuse 11.1 machine today):
Before you start, make sure, that your network settings are OK and you can ping both machines from all directions
Next make sure that the time for all involved computers is identical (Kerberos is very picky when times differ. That is for security reasons to avoid logins with sniffed packages.)
So it is best to configure ntp to keep the time in sync.
1. register your domain-controller in the machines hosts list via Yast or with editing /etc/hosts
Insert the fully qualified domain name first, then the short name as the alias.
192.168.1.7 server.domain.com server
2. edit the /etc/resolv.conf and add your DC as a nameserver
nameserver = server.domain.com
3. Open YAST and configure Kerberos.
The realm has to be written in capital letters
4. Configure SAMBA with YAST. Domain controller option is set to none (not
PDC or BDC). Workgroupname is your domain.
Edit the /etc/samba/smb.conf and change the security from "users" to "ADS" and add a line "realm = DOMAIN.COM"
Then don't forget to restart the samba server.
5. Execute the following command:
net ads join -U Administrator (<-- use a domain user, that is allowed to add machines to your domain. So why not the Administrator
6. Now open YAST and choose the "Windows Domain Membership" option.
Domain membership should be already your domain.
Check "Use smb-information for authentification" and "single sign on for SSH" (if you want it).
After pressing OK, Yast will install winbind and some other necessary packets.
7. Reboot the linux client and go and get a coffee.
8. Now you should see additional options in your logon screen.
<local>, DOMAINNAME, CLIENTNAME
Choose your domain and logon with your domain user account.
Thats it - the rest is finetuning (for example mapping the users home to the domain-controller or something like that).
I will write a longer version of that for my homepage linuxpeter.de as soon as I find some time to do that