DO NOT grease it up or take it apart - greasing will not remove old grease that is hardened, and disassembly is out of the question - time intensive, likely to lose bearings or parts. Best to have a shop remove the freewheel (don't remove any guards or spacers underneath the freeewheel). Dunk it in solvent and spin until it runs free, then just follow Sheldon's lubrication advice: http://sheldonbrown.com/freewheels.html and reinstall it if it now works OK - no tool required, just carefully screw it on. (handy hint - turn it counterclockwise until it seats into the entry threads, then clockwise til it stops. Riding will tighten it.