1. Visit syphon.v002.info
2. Download the Quartz Composer plugin from the link on the right
3. Follow the instructions in the Read Me to install the plugin
4. I don’t use Grand VJ, perhaps the Syphon Client QC.qtz included with the Syphon QC plugin will just work – if not, ask the GrandVJ folks (and suggest they add native Syphon input).