Safari AdBlock 0.4.0 RC3 now works on Snow Leopard.
To make it work, though, you have to run Safari in 32-bit mode. To do so, select Safari.app in the Applications folder, hit ⌘-I to show the “Get Info” window, and check the “Open in 32-bit mode” checkbox:
I’m looking into an alternative solution to allow Safari to run in 64-bit with AdBlock (and any InputManager) enabled.