ATI Mobility Radeon HD 3470 & HD Video

[CowboyHacker]

I have a Toshiba Satellite A305-S6841 with an ATI Mobility Radeon HD 3470. (Win7 x64, Intel Core 2 Duo T5550 @ 1.83GHz, 4GB RAM)
THe problem:
I tried playing a 1080p video
VLC stuttered and the picture would freeze and pixelate (much like a dirty DVD)
So, I tried it in WMP, and it plays (latest DivX HD installed), but the video lags and bit and gets off the audio and doesn't catch up.
My video does support ATI Avivo HD playback, according to the specs on ATI's website.
There is a new video driver available, Version 10.x, but ATI won't let me download it because Toshiba does the drivers for my system.
Toshiba's website shows the version I currently have installed- V 8.6.

Would the new driver work better? If so, how can I get it?
My CPU load was no greater than when playing a standard resolution file, and never maxed out. The cooling fan did come on, as it does when I play 720p content.

The file I'm trying to play is an .mkv, if that helps.

[Kphu]

I have the same laptop as you. I would love to see an answer for my future reference.

[CowboyHacker]

I haven't found one. I gave up on 1080p. Back to 720p.