Bill just beat me to it, but the FishFillets plug-ins are very old and the VST versions of them are also for PPC Macs only. So they won’t work on OS X 10.6 (which is an Intel system). The way to check (I think) is by right-clicking > Get Info over the Fish Fillets.component file.
I think your only chance is to install Rosetta then find an audio host (VST or AU) that is a native PPC application rather than a Universal Binary like Audacity. You could try running Audacity under Rosetta, but I don’t think it will work.
If you update to OS X 10.7 then there is no support for PPC programs whatsoever.
Gale