I think almost any PC with core duo 2 CPU are enough for perfect H.264 decoding...
I have CPU: Intel(R) Core(TM)2 CPU 6400 @ 2.13GHz (Family: 6, Model: 15, Stepping: 6) and picture of "x264 recording VIDEO: [avc1] 1280x720 24bpp 23.976 fps" is just perfect, but sound comes out about 0,2 second too early with xine.
With my other machine "AMD Athlon(tm) 64 Processor 3400+" can not play those file with-out heavy problems, totaly under power CPU for that kind of playback.
My friend has a configuration
hard: Asus P35 + Intel 2160 @ 3GHz + 2GB ram (@800MHz) + SATA disk + ATI2600XT 256MB + TT3200 soft: debian testing (lenny) kernel 2.6.22-2-686 V4L-dvb = Multiproto - 26.10.07 xorg video driver = ati 8.41.7 (fglrx)
vdr 1.5.10 + vdr-1.5.10-dvbs2-h264-syncearly-framespersec.diff xine-0.8.0 plugin
ffmpeg-cvs from 08.11.2007 xine-lib-1.2 from 8.11.07 xine-ui from 8.11.07
and can see the h.264 dvb-s2 channels with average 60% CPU load.
Igor