Okay people, here's a quick lesson in home wiring: don't put half of your house on one circuit. This is what we call a bad idea. Seriously, I have counted 9 outlets, 5 light fixtures and a microwave all wired onto one 15amp circuit. I'm amazed that I've only had it trip once. Seriously folks... if you're going to do some electrical work around the house, at least do a little tiny bit of research. 15amps = 1800 watts. A microwave? 1000+ watts, a hair dryer 750-1500 watts (one of the outelets is in the bathroom). Just these two things alone are a bad idea, let alone everything else.
Okay, that explains why whenever a hairdryer runs in my house, my bedroom light dims. I never knew they took that much power. If I ever take up amateur electricianing, I will not do this. I probably won't ever be an amateur electrician, I would be too afraid of messing something up and it isn't an area I'm particularly gifted in. But good for you for figuring it out! Now can you fix it?
My plan is this: Rewire two of the outside lights onto another circuit (should be easy). Rewire the Microwave onto another circuit (more difficult but very challenging). I might even rewire the dining room light too, but that would be more challenging and less beneficial (its 300watts, and not often used in at the same time as bedroom/bathroom stuff).
Holy God in Heaven! Why would anyone wire a house in such a manner!? That is seriously a bad idea. Good luck with the rewiring.