Last night, I loaded Vista Ultimate on my laptop (Alienware m9700, Turion ML-44), and my system began to overheat, making my system auto shutdown. Now, the longest uptime i can sustain is 10 minutes (even when idle) without using a real fan to blow at the base of my laptop.
The thing here is, I had managed to play World of Warcraft on Vista at the start of this year for at least 8 hours straight, when Vista was just released. I reverted to XP though because my video card drivers were not very compatible at that point of time.
try checking the power options. power options > change plan setting > change advanced power setting. i particular the cooling options. i have a toshiba laptop and had to install a toshiba vista power options addon to access the special power saving and cooling features.