I installed a few games onto the Vista partition the other night, in particular, Splinter Cell Double Agent, Supreme Commander and Company of Heroes.
Both Supreme Commander and Company of Heroes worked right out of the box without any trouble, I loaded both of them and tried the tutorial missions and they were both working out ok. I didnt play around too much with the graphics settings yet - I'll mess with those on the weekend. In COH I did try turning everything up to full just to see and the game was still quite playable, a bit sluggish now and then but playable.
Splinter Cell was a bit more interesting in terms of installation and setup. The initial install went fine but took a while, once complete though it asked me to install directx9c which being on Vista I refused. IT them promptly popped up the hardware detection utility and informed me that I didnt have the correct version of directx, graphics drivers and something else which unfortunately my tired brain can't remember at the moment. The long and short of it though was that I wouldnt be able to play the game.
I didnt believe as I had already played the game on this same computer on a Windows XP partition, so I knew it worked. So I simply cancelled the hardware utility and tried running the game and it ran quite happily with no issues that I could see, although I only tried the first 10 or 15 minutes of the first mission.
One thing to note here though is that the game ran better than it had under Windows XP. On XP I had a problem that the game was incredibly slow - I had to disable one of the processors in order for it to be playable (go into task manager, right click the game process and choose affinity). On Vista it played quite happily from the start without me having to make any changes.
I'm hoping to get some time to play during the weekend, so I will try tweaking graphics etc then and let you know what I found out. In the meantime I thought that this might be useful information for someone, even if its not very scientific ;)
Update : Thought it might be useful to post my machine specs for reference;
Macbook Pro, Core Duo 2ghz, 2GB RAM, ATI Radeon X1600 256MB