It's been a while since I changed pins/bushings, but I do seem to recall the bushings being a pretty snug fit in the hinges - they rely on an "interference fit" to keep them in place.
Best advice I can offer without actually seeing the installation first hand is to make sure the bushings are going in square (check before you start to press them in and make sure you are pushing straight down on them) and try a bit of oil on them.
Also, check to make sure there isn't a burr or piece of the old bushing in the hole.
Sorry I can't be more specific - good luck, and if they are really being stubborn, resist the urge to use a bigger hammer!
I just put new bushings in my S-10 door hinges. Came up with a nice easy way to get them in straight and no chance of bending the hinge arms either.
Use a socket that is a bit bigger than the hole the bushing goes into. Use that on the side opposite the flange on the bushing. Put a bolt with a washer under the head throught he socket and up(or down) through the hole in the hinge and the bushing. Another washer and nut on the flange side of the bushing. Now a couple wrenches, tighten the nut and press the bushing into place. If you have any trouble getting the old bushing out, use a socket big enough to clear the flange, grind the corners off the head of the bolt and use a nut and washer on top of the socket to pull the bushing. You have to grind the head down enough to clear the hole in the hinge as the bushing pulls out, but again, this works great and no beating and messing up the hinge.