I'm playing Civ IV (BTS) on a MacBook Pro 17" with 2GB Ram in bootcamp.
I've downloaded SMC Fan control and it seems to help some with the crashes (I set it to max fan speed then reboot into WinXP it retains the fan speed). I've also built myself a custom notebook stand that raises the back of the MBP 2" off the desk and then rigged two 4" computer fans to blow cold air directly onto where the video card is on the MBP. Doing it this way I can often play for hours without crashing.
However, I still get random sound repeating, lockup reboots. I think that's something different than the complete reboots.
I think the complete reboots are due to overheating and the sound looping crash is due to some driver incompatibility.
TRM
P.S. - The total cost for this notebook stand setup was about $20, consisting of 1 2x4 that was cut to 6" and bevel cut one end at 45 degrees (the edge of the 45 degree cut is where I set the center of the back of the laptop) to provide stability and keep good airflow and 2 80mm fans that I hard wired on standard 4 pin HD connectors and then used this:
http://www.cooldrives.com/saandidehadr.html with a 1to2 power splitter to power it. Rigged up but it works to keep it cool.