Take the new JFK AirTrain to the subway (the E train), which will drop you off about 3 short blocks from the Club Quarters. Cost is less than $7 and travel time is just about an hour, which is about as fast as most other options, depending on the time of day.

There are several threads on the topic - here's one recently:
http://www.flyertalk.com/forum/showthread.php?t=400157

[edited to add]
Oops - didn't realize you're at the downtown Club Quarters.