Thanks synapse and Baldrick65 for your comments.
I didnīt manage to install Firestarter from source (dependancy hell) or find an rpm for SuSE 9.0 but I then did find a SuSE rpm for guarddog and the rest was a breeze. Set up the thing in 15 minutes, all ports sucessfully stealthed, Samba for the LAN worked immediately. Very, very nice.
Hereīs the URL to the download, if anybody else is interested: