HD stuttering using Intel IG35 WDDM 1.1 driver

I have an HTPC with an Asus P5E-VM HDMI mobo with IG35 onboard graphics and a E8400 Core 2 Duo 3 GHz CPU with dual boot Vista 32bit and W7 32bit setups. HD works OK under Vista 32 bit using the latest Intel Vista driver but it struggles under W7 using the WDDM 1.1 driver automatically installed by Windows.

The stuttering is fairly random but occurs very frequently and most likely due to the CPU maxing out under HD resolutions (as I assume most of the graphic processing is being done in software). When I look at CPU performance while displaying HD, it shows that the CPU is working very hard. If I set the screen resolution down to 1024x768, it copes OK.

Should there be some hardware graphics acceleration with the onboard GPU under the W7 driver or does it have to rely heavily on the CPU? I don't understand why my CPU is not coping as it's a good spec. Are there any tweaks or settings that would improve things? I cannot understand why performance under Vista should be better than under W7.

If I can't get it to work properly, I might have to put back in my noisier HD 4670 512Mb GDDR3 card to take the load off the CPU which I shouldn't have thought to have been necessary.

Any help would be appreciated.

Thanks NosferatuX, I'll try that. I think I will need to temporarily disable automatic driver search otherwise windows will keep trying to load their driver before I get a chance to replace it.

I noticed that in disk manager only c: said active on my system, so Ive set all the others to active as well, not sure if that could be a reason.

Well, I uninstalled the WDDM 1.1 driver and replaced it with the latest Vista driver (after disabling automatic driver search) and all seemed to go OK except that I couldn't get full screen TV on Zoom 3 setting anymore. It just increased the picture height a little but retained the black bars top and bottom. Added to that, BBC HD froze after a second or so each time I switched channels so I would conclude that the Vista driver is not suitable to run under W7.
So it's back to the drawing board.
I still need to play around with the graphic settings using the 1.1 driver as I think that when I switch off the plasma screen and fire up the projector instead, it goes into dual display mode. When I set it to the projector display only, the stuttering seemed to stop but I didn't get enough time to play around with it to be sure (my wife wanted to watch the news!).
I will probably also look at reinstalling the Radeon 4670 card and see what results I get by comparison.

NosferatuX said:

Interesting. I'm sure you know that marking a partition as "active" means that you are telling the BIOS that it contains an OS on that partition, which is marked by some partitioning tools as active by default. Disk drives that is used for storage purposes does not require/necessary to mark any partitions as active whether it be single/multiple partitions.

hmm so perhaps I should un-active them.

Well. I've since put in the HD 4670 card with the new Catalyst beta driver which allows me to set up profiles in CCC which I'm playing around with. The only downside is that I could here the fan running on the HD 4670 rather than the silent Intel onboard setup. If anyone else finds this annoying, I fitted a Zalman VF1000 ultra quiet cooler which is virtually silent now and cools better than the original cooler that comes with the card.
The picture quality has improved significantly with a bit of tweaking such as changing the colorspace and applying some edge enhancement. No stuttering and very smooth now. Almost fooled into thinking SD is HD on my 42" plasma!