You can set up 1 to 1.5 TB SATA RAID 0 inside your G4, if it is a Quicksilver 2002 or later.
Two 500 GB or 750 GB SATA II drives and a controller that works in G4 PCI slots.
That will allow you to do multicam with several tracks of video and audio.
Also that can do at least 2 Standard Def video streams.