have anyone tried playing MP4, which length about 23 minutes with sizes around 230 MB on a Pentium 4 2A GHz with 512MB ram ? I played it with WMP10, the CPU usage has reached up from 65 to 100%, it make some scene is lagging of sound by 2-3 secs, this can be determined during the OP of the anime.

When I run the old mplayer2(not media player classic), problem seems resolved a bit, but the CPU usage still around 45-99

does MP4 with class 10 AVC really need some high end processors?

Its no surprise that you get those high cpu usages
AVC needs powerful processors to run smoothly
Try HD resolutions and see your comp lags throughout the video

For the decoder, I recommend you to use CoreAVC as its the one of the fastest decoders out there but with low requirements like that, even with CoreAVC, its better to avoid HDTV videos with AVC

I am using CoreAVC included in kLite, I need to turn off all firefoxes in order to view smoothly