Thanks everyone for all your replies. I already have my physics fixed at 60Hz, so I guess I'm already doing the right thing. For some reason I was starting to think that I also needed to fix game play logic to 60Hz, but it appears not.
I guess what I'm wondering is if my game logic is running at 100Hz and I need to add a velocity to an object, which will later be simulated by physics at 60Hz, I will need to scale that velocity first by 0.01 right? (1 second / 100Hz)?
BTW, I know this is the multiplayer forum, but my questions are in regards to syncing the game across the network so the simulations appear close enough :-)