You can take a stab at Twixtor, but you're asking a lot here. At 24p, 50% or 70% reduction takes you to 12 or (roughly) 7 frames per second respectively. Not the recipe for smooth motion.
the best slow mo your going to get at 24p is at 80%. With 60i you can slow down to aprox 50%. If you have after effects there are some ways to smooth out slow mo.