I had been using C4D on a “Quicksilver” Dual 1Ghz G4, and it would temporarily lock up during rendering with Leopard.
However, I recently got a new MacPro and it does not have the issue. It could be the build of Leopard on the MacPro, or just that its a much faster system. Since someone else said they experience the freeze on a G5, I am assuming it’s the newer build of Leopard on my system that fixes the problem.