I've had a couple messages about the method I used to free the New World seat post. This was the Kroil and small torch method.
The method I used was really a last resort, or near last resort for a very difficult seat post. There are other things you can do before you reach the heat and Kroil phase. Sheldon Brown's website discusses the methods in more detail, and in the order to be tried.
I detailed the Kroil and heat method merely as an example as a really difficult case- it's not where you'd go first. However, if you have a very, very stuck post, you can go that route. It applies only to steel posts, like that on the New World and other vintage bikes.
"If nothing else works to free up a steel or titanium seatpost, the
next-to-last resort is to heat the seat tube up with a hair dryer or
propane torch. This should be done with great care so as not to do too
much damage to the paint. You should work as fast as you safely can,
because you want to heat the seat tube so that it will expand, but if
possible you should quickly put the torch down and start pulling on the
saddle before the heat works its way through the seat tube and makes the
seatpost expand too. The torch technique is worse than useless when you are dealing with
an aluminum seatpost stuck in a steel or titanium frame, because
aluminum expands twice as much as steel, and 2 1/2 times as much as
titanium for the same increase in temperature. In fact, the exact
opposite technique will often do the trick for aluminum seatposts --
cool the seatpost down as rapidly as possible. The contents of a CO2
tire inflation cartridge applied inside the seatpost can shrink it down
just enough to do the trick. [As will dry ice, which is also CO2, and can get the seatpost colder-- John Allen]" (from the above Sheldon Brown link)
The above link is a good reference and certainly worth trying.