Here is a site for you that explains how the system works:
http://www.diydata.com/planning/cent...g/pipework.htm
and another
http://www.diydata.com/planning/cent...ing/boiler.htm
It's not that complicated. You need to turn off the boiler, drain the system, and then start ripping out the plumbing.
To drain the system you will need to open the return pipe and send that water out of the basement (or wherever your boiler is). To make sure it drains completely you will need to open a vent at the top of the system to allow air in to replace the water going out. THen it's just a matter of disconnecting the radiators and removing them.
Selling them as scrap should get you a decent chunk of $ as well.