1. Best method of getting tough nuts/bolts is to use a LONG LONG LONG extension. Doesn't have to be anything special... even a long metal pipe would work. Just stick the handle of your ratchet into the pipe and it should give you enough leverage and torque to get that sucker off.
2. Like they mentioned above, use LOTS of Liquid Wrench, PB Blaster, or WD40
3. New gaskets are ALWAYS recommended if you are taking apart pieces that are exposed to lots of heat (engine parts, exhaust parts, etc...). You may be able to wing it with the old gasket on there if your car is fairly new.
Xam - 2004 WRX - Cobb Stg II - Ugly Ricer Spoiler