zoo tycoon 1's game engine is not that good and can not handle many things in the items list.
it can crash because you have too many things loaded in to the update folder for it to find and load in to the games item list.
this is why they made zoo tycoon 2 with a bigger engine. only they added more things for it to do which makes it act like a small game engine also. or it does seem that way at times.
but that is what is going on with zoo tycoon 1 crashing, there are also some issues with the free form zoo maps being too large. or just having a custom map made with a kit that allowed you to change it to your own liking if you removed too many sections of the outside zoo wall it crashed. all seems to point to the game engine not handling too many user items.
of course then you have items that were not made to work with other user items and if you mix them up the game can crash. but most the time they just make it do strange things. like water coming out of a phone booth instead of a foutian? not that i ever seen that but it might happen, i did have the video arcade game where it loaded up hundreds of people in it, the game was letting them in and not letting them out.
most of us just have scanned through the old items and removed them one at a time until we get the ones that work on our computers. and toss the ones that don't.
hope that helps you.