Martin, I had the same problem when I tried running FM 6 on Snow Leopard - it worked OK except for the Web Companion.
I have a feeling that you're not going to get this running (FM6 on 10.6) - I think your best options are to downgrade to 10.5 or upgrade to the latest version of FileMaker.
Thanks for your reply Jesse. It'll probably sound like a stupid question, but how do I go about downgrading? I've only ever upgraded before!
Hi Martin - I'm not sure either, but my guess would be to run the 10.5 installer and select the option to archive previous system folder, in the custom installation section.