With that kind of hardware, is hardware decoding and encoding of media a possibility? A DLNA server with hardware transcoding is something I've been thinking about recently.
You can use AMD graphics cards with their open-source drivers. I'm not sure how well hardware-accelerated video works with them but it should work the same as it does on x86 Linux. Multimedia is probably one of the weaker areas for Power since there's so little focus on writing Altivec SIMD code for the platform from the larger open-source multimedia community (most of their focus is understandably on x86 and ARM), though that wouldn't impact hardware en/decoding.