If the stem goes into the fork and there is a large exposed nut at the headset, its threaded. If the stem clamps to the fork and has a bolt where the top of the fork would be, its threadless.
http://bicycletutor.com/overhaul-threaded-headset/
Can you take some pics of it? Would help determine what's on it. 1, 2, and 3 piece cranks come apart differently but its all simple stuff. Look at the crank arms and see how they attach to the spindle or if there are no bolts pinching them to the spindle.
http://www.danscomp.com/serve/faq/cranks_faqs.htm