You should only use a Dremel if you already have one, don't buy one just for this. Otherwise, a 3" hole saw/drill will work just fine. Criculation in your case is definitely an issue, I cannot stress enough your need of case fans. Install them in the top of the case (if you can) too...And consider drilling two holes in the side of your case, one blowing in and the other out. This will produce fresh air over your CPU & Northbridge all the time.