The key to using a heat gun for any type of repair is preparation and patience. There is a difference between the heatgun used to strip paint off of a car and the one used to work on PCBs. As was mentioned above, pre-heating the entire board to prevent warping is a must. You also need to carefully cover parts like capacitors and connectors with a heat shield like foil to prevent damage. Take your time and SLOWLY heat the components necessary to re-flow their solder points.
If you get is a hurry you'll turn your board into a taco, and ruin any chance of fixing it. Lastly, for the love of god, never NEVER put it in a household oven. Yes, there are ovens for PCBs, but they are specialized for exact temperature control and heat profiles to prevent damage. Attempting to "bake" your board will only result in a melted pile of plastic.
I have repaired many many xbox 360's with RROD using the correct heatgun and a lot of practice. You can do it, if you take your time.