gtapolicetrucker

i think you look at the poly count of vehicles with openiv 
also the original vehicle poly count is around 20k to 30k polies
i doubt you'll find a police vehicle around that range since most are pretty high poly but you can look around and find what your looking for

they're multiple tutorials showing you exactly how to import textures
i myself have made a whole entire tutorial showing a multitude of things
number one you don't have texture loaded into the texture browser, and if you do make sure that they're all in the same format
also when your import make sure you select what type of format your images you have, on the bottom left there should be a drop down list of types of texture
png,dds,tga select what ever one your textures are in
also as I've said before when your importing models into zmodeler make sure you have sliced model selected or else your whole entire model will be one big blog and the dummies will be messed up.

replace your zmodeler profile with the oringinal one
zmodeler loves to touch things that it shouldnt

did you name the material rear window guard cause if you did then thats you problem all together.
i would to name something more appropriate such as mesh, or vehglass and then let zmodeler rename it to rear window guard mesh or whatever upon reimport.