New Puppy to a house w/ 2 cats

I have 2 cats and I just got a new puppy. The cats did not like the puppy the first couple days, they did the whole hissing and scared for their life routine.  The puppy just wants to play, but the cats really take offense to anything the puppy does.  I realize the cats can really hurt him, so I keep them under close supervision. They are in seperate rooms when I'm not home. When I am home, the puppy in in a huge playpen so the cats can observe him, but the puppy cannot invade their space and just jump on them.

Does anyone have any tips on hopefully encouraging the cats to accept the new addition to the family?
Any suggestions, tips and personal experiences would help me out a lot.
I love my kitties and I hope they will accept him and not hurt him.

Thank you guys for your help !!