How can I cook 1/2 a cup of rice?
When you microwave on full power you are likely boiling off all the water before it can be absorbed by the rice. When you cook rice on a stove a common method is to bring it to a boil and then turn it down to low, cooking it until the rice is done. I prefer this method as I like the texture you get and once it's cooked you can eat it straight away without any extra process. I would suggest you mimic this method with your microwave by starting on high until it boils and then turning the power way down until it is cooked. On the stove this method requires you cover the pot, not a practical option in the microwave so you need to add some water to make up for the moisture loss. 

Another way to cook rice on the stove is to add much more water than you need to cook the rice and boil it until the rice is done, then drain the rice while discarding the extra water. You could also try this method in the microwave very easily. The drawbacks to using this in the microwave is that if it boils over you will end up with a puddle of water on the bottom you have to clean up, and you still have to drain it. 

So my advice for dorm room rice is the first method, you just need to experiment with water levels and power settings.