I've done so many of these, I now have a standard procedure.

1. PB Blaster
2. Propane torch for 5-10 minutes.
3. Air impact wrench for 15 seconds or so. The 425 ft. lbs mine supposedly puts out is rarely enough to break them loose, but I think the impacts help to loosen things up a bit.
4. 30" breaker bar w/ an impact socket on the end. I usually have to stand on it and bounce violently while swearing at the car. When it does come loose, it usually feels and sounds like you've broken something. Hopefully you haven't.

EDIT: Ratchets aren't really meant for that sort of abuse. Since they're Craftsman though, take them back and tell them you don't know your own strength

 

A T-Bar is better for the job get a good impact socket. Then get a pipe onto the end of the bar and apply pressure, and with a hammer give it a good few wallops at the back of the socket to wake the nut up.

Job for two

 

I have a good impact socket, but the nut seems to have shrunk due to rust, so I may need to get a smaller socket.
I'm not familiar with a T bar, where can I get one?
Is 1/2" drive beefy enough for the job?

 

http://www.flickr.com/photos/8492055@N08/2966276390/

The item at the bottom of the picture, also known as a sliding socket bar. It
will take more strain than a ratchet, I've opened them nuts with half inch drive sockets before so they should be able for it.

 

My hotrod building Dad sent me this a while back, I found it interesting and maybe worth a try in your situation:

Machinist's Workshop magazine actually tested penetrants for break out torque on rusted nuts. Significant results!

*They arranged a subjective test of all the popular penetrants with the control being the torque required to remove the nut from a "scientifically rusted" environment.*
Penetrating oil ..... Average load

None ..................... 516 pounds
WD-40 ............. 238 pounds
PB Blaster ............. 214 pounds
Liquid Wrench .. 127 pounds
Kano Kroil ............ 106 pounds
*ATF-Acetone mix....53 pounds

*The ATF-Acetone mix was a "home brew" mix of 50 - 50 automatic transmission fluid and acetone
*Note the "home brew" was better than any commercial product in this one particular test. A local machinist group mixed up a batch and all now use it with equally good results. Note also that "Liquid Wrench" is about as good as "Kroil" for about 20% of the price.

 

I would love to mix up a small batch of Acetone/ATF, but what on earth can you store it in? Any plastic oil containers which can squirt it out would probably be dissolved no?

 

I think he means to get a breaker bar but if it was me I would definetly use a propane torch on it first.