I have the same laptop and I'm experiencing the exact same problem as you describe. I'm only having the problem though in youtube which is the same as you're experiencing.
I have done a clean install of Win7 Ultimate x86 though with 2GB Ram. The laptop behaves perfectly except for this youtube problem. I'm running the ATI Express Catalyst 10.2 drivers
I found this link interesting but it relates to Win7 x64 and different hardware.
http://www.overclockers.com/forums/showthread.php?t=642390
I'm game to give this fix a go but can't do so immediately repost if you try it out before me and let me know if it works for you.