:)
It will be useful if you tell other users how did you make the videos play properly.
I think the creators of these clips have tried to squeeze hi-res content in a bitrate apropriate for PAL resolution. I noticed many compression artifacts. The bitrate alone will not require a very fast computer. Your machine will probably be too slow for H264/AVC decoding at regular 1-2 MBit/s. H264 is a very good format and achieves its quality at expense of CPU time.