This is really easy to do. The SSH server is set up to run by default, all you need to do is open the firewall port to allow access. To do this (I'll use the universal method for both Gnome and KDE), open a console window and type su and then press enter and type your root password.
Now type yast2 & (include that '&'). Click Security & Users and then Firewall. On the left, choose Allowed Services. Under the Service to Allow box, choose SSH and click Add. Click Next then accept.
You should now be able to administer this box remotely. From another Linux system, go to a consol