You'll want the Intel not only for its speed and video features, but also because the PPC Macs are nearing obsolescence. Snow Leopard, which only runs on Intel systems, provides a nice speed boost and frees up hard drive space when compared to traditional Leopard, so you'll have a better experience overall. This is important when dealing with multimedia, as you'll want a responsive system with plenty of room for storing iTunes files (if you will be buying your movies through the service).
Additionally, keeping your machine up to date when using multimedia technologies is key, especially components such as QuickTime. When a major version change occurs, expect some of the older models to get left behind, especially the PPCs. Veteran Mac users may remember this happening with the 680x0 to PPC transition in the 1990s. The first PPC models appeared in early 1994. By late 1998, nearly everything was PPC only (including MS Office and the Mac OS, which was at version 8.5 at the time).
Apple also declares hardware "vintage" or "obsolete" quicker than in the past. The days of being guaranteed repair parts for a 12 year old Macintosh Plus are long gone. Part production is usually halted five to seven years after the computer itself is discontinued (although parts are always available in California for seven years due to a state law). Keep in mind that Mac Minis with G4 processors were discontinued in early 2006, about three and a half years ago.
At this point, a G4 computer's long term future best projects it as a backup machine for an Intel Mac, a computer for your children, or as an extra computer to use in the kitchen as a CD player and recipe book. Like the 68040s in 1998, the PPCs will probably be extremely tough to find modern software or software updates for next year at this time. They will still work fine for practical applications (I still use an iBook G3 for word processing), but for multimedia, where updates are key, you'll want something capable of running modern software and accepting updates to keep services (such as iTunes) working.
