Installed and running on my HTPC now.
P4 3.0GHz
1GB RAM
A large IDE hard disk (120 maybe)
Gigabyte P4 Titan GA-8IPE1000Pro
Radeon 9800pro
Sound Blaster Live! 5.1
Obviously x86 version here. Installed much faster, and was easier than Vista, boot up time must be about half that of Vista, about 2/3 of XP. It picked up all the drivers except the sound blaster on installation, but when booted proceeded to automatically install the sound card from windows update. However, this driver had problems with sound distortion, much like in Vista, but a different modded driver and changing to 5.1 (on a 2.1 setup) sorted it, albeit with low volume. Will probably go back to the onboard realtek, though it has noticeably poorer sound quality.
Apart from that one niggle, its running extremely well. Using NOD32 for A/V with no issues, and all progs have worked fine so far. VMC also works nicely, there are a few decent changes from the vista version too. Had a little bug with the start menu showing VMC as open when it wasn't after having closed it though. IE8 works well enough, and the window dragging features are a godsend with the widescreen tv it's hooked up to, wish I had them in Vista on my main machine.
Can anyone recommend the best ATI drivers? Not essential since Aero was up and running fine on first boot, but might be nice to stick a couple of games back on there.
All in all, very impressed, if it carries on improving I will be buying this for my main machine certainly.