Well that's what I was thinking; but it runs like !@#$% on this machine. It's the only video type that I have issues with too.
My (relevant) specs-
Processor: 1.66GHz dual core
Ram: 1Gb
Video: Mobile Intel 945 Express
Hmm... Have you tried using VLC Player playing these videos? I tend to download my anime encoded with x264(commonly referred to as h.264 for those who don't know) at 1280x720 and they play fine.. even streaming over the network.
My specs are:
Processor: 1.6ghz Intel Celeron M
RAM: 768MB DDR2
Video: Mobile Intel 915 GM
Your laptop is superior to my setup and it lags... that's odd. But yeah, try watching the videos with VLC Media Player and see if they lag. FFMpeg sometimes can be weird :S.