Yeah, was afraid of the rusty bolts. Best bet is to spray the bolts with a penetrant while the engine is warm. Follow the instructions, which usually say tap on the bolt a bit to set up vibrations which help the oil to penetrate. I would do this several times the night before I wanted to get to work and again before I started working on it.
Liquid Wrench works OK, Silikroil or Kroil from Kano labs works, something sounding like PB Blaster seems to be a favorite of some of the guys.
A broken bolt is a real PITA especially if you don't have any room to work in.
Remove the bolts carefully. Maybe a little heat from a propane torch may help.
If lord forbid you do break a bolt, let's hope it leaves eomthing to grab on to. Then various tricks can be tried. Some recommend heating the bolt til it is very hot and then touching a candle to the threads so they wick up into the rusted area. Some recommend welding a nut to the bolt and then removing.
If you have to use an easy out DO NOT break it, or then you really have a problem. Some recommend a reverse twist drill instead. They drill the hole and a lot of times will cause the bolt to turn out due to heat vibration, torque and luck.
If you do break the bolt, check this website for discussions on how to remove.