h264 playback problem

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My laptop is an asus x51r. Processor is Pentium Dual Core and I have 1gb RAM. I use CCCP FFDShow for my codec needs and I noticed that the video lags when I play 720p h264 videos with karaoke'd softsubs... I then noticed that the player uses around 100% of one core and uses virtually 0% of the other. So I changed the number of threads in FFDshow's video decoder options and voila! The player now uses about 40% of the other core. However, the video STILL lags when I play the said video. So I decided to try CoreAVC. That solved the problem of lagging video and the subs are now in sync with the sound. HOWEVER, this time, the video would have weird lines on it, like the frames overlap or something. What could be the problem?