Hi Hmmrm,
I know that this thread is pretty old, but I just wanted to post his incase anyone else comes across it or you are still having this issue.
1) By default Windows has some energy-saving settings that cause the Mac to use passive cooling (without fans) in stead of active cooling (with fans).
When you first install Boot Camp, there is a very high probability that under some conditions your Mac will use passive cooling, which would cause sit to get pretty hot.
All you have to do to fix this is change the setting in the Control Panel; see this site for details on how to change these.
2) But the thing that will help most is dialing down your CPU. By default, Windows is set to allow you to use 100% of your CPU. This is good for short CPU-intensive tasks, but if you're playing video games for an extended period of time or doing some serious long-duration work, it can make your computer get very hot (and waste an unnecessary amount of energy).
I usually keep my max cpu power between 73 to 93% when working and gaming, but I have quite often taken it down as low as 30% while doing mundane internet and text-related work, without any serious loss of productivity. Gamingwise, I would recommend you start at 75% and go up or down from there based on your own judgement. You can access these settings by going to Maximum Processor State in the same window that you used to turn on Active Cooling (see the above link).
This article talks about these cpu power settings as well as some other suggestions. I agree with most everything they say (though some things are a little unnecessary). I would caution you about Tip #3 though; it is true that this does help temporarily, but in the long run it only delays the inevitable as I am about to mention below:
3) Make sure your computer is 100% charged and plugged in when you start playing. The reason this is important is that if you start running low on battery and decide to charge your computer while playing, you will be putting a lot more thermal load on your computer. Not only will you be drawing a large amount of energy for the CPU but you will also be drawing power to charge the battery at the same time.
4) I should mention that I crashed my old laptop many times due to overheating, and it still works perfectly even to this day (and that computer is more than seven years old!). So yes, overheating can be bad, but computers nowadays will generally turn themselves off before any serious damage can be done.
5) As mentioned in Tip #5 of the second link, use a cooling pad. Those things are wonderful. I almost never do any long duration CPU intensive work without one. It does not cool you computer down all the way, but, buying this cooling pad stopped the heat-related crashes on my older laptop so now I use it even on my new MBPr, just in case. 🙂
Hope this helps!
Vlad
