ahh okay now its clear for me what you mean. however i wouldnt do it that way even if you do checks at the server. i cant await seeing a demo of your game to test this. i learned in serveral threads that this causes the simulation to diverge and brings big problems.

you should be able to get closer to actual positons at your clients if you extrapolate the position of the other clients a little bit ahead of their current position. if you make this relative to the speed you shouldnt have too big problems. so your client player gets the current position from the server along with the current forces of that object and extrapolates a position ahaed of time that compensates the lag time.
you can even use the dplay_latency variable for that like lokoweed suggested so you should be able to predict almost perfectly where the players are at the server - even if you get the older positions and forces only.