http://www.almico.com/speedfan.php
You can also check your idle temperatures in the BIOS, if your motherboard supports hardware monitoring.
Get idle temperatures and "load" temperatures:
1) Idle: Just check out the temperatures while not doing anything
2) Start the game, enter a map and play for 5 minutes. Alt-Tab into Windows (don't worry if Starcraft crashes or anything). Then take a peak at Speed Fan to see where your temperatures are. You may have to be fast, since CPU/Video card use will drop off precipitously once you alt-tab. Notice the CPU, motherboard/case temperature, and hard drive temperatures. Report back here with them.
Alternatively, to get load temperature, you could run something like 3dmark (which is free) and benchmark your computer. While it is running the benchmarks, have speedfan open and monitor temperatures.
Also, you could run something like SuperPi (free) to stress out your CPU and see how high you can get the temperature.
This will tell you whether or not your computer is approaching the auto-shutdown threshold.
If it is, you will need to probably reseat your heatsink fan with new thermal paste, or investigate other cooling options.
For example, my motherboard is Asus, and it comes with a utility to monitor temperatures.
IDLE:
CPU: 38C
MB: 36C
LOAD: CPU: 49C
MB: 46C
This is well within normal ranges. If my CPU was in the 70-80C range, I would suspect I had a problem with my heatsink fan. 80C is a normal auto-shutdown point that gets triggered to keep you from frying your CPU.