Will 18" rims with 245/40/rz18 fit on a 2000 dodge neon

Why?
Don't know the answer to the question b/c I haven't tried it.
But why? Neons are underpowered to begin with. Adding 18" wheels is going to seriously cut into the acceleration and put a strain on stock brakes. Handling is always a debate, on stock bushings and alignment, I would say 18" wheels would degrade handling considerably. If you have upgraded to coilovers and polyurathane bushings I would say 18's may be an improvement.
Most people have found 16" wheels to be about the largest you would want to have on a Non-Turbo Neon. SCCA racers use 15x7" wheels mostly.

try tirerack.com

[quote=neon_rt]Why?

I'm with Neon_rt...what is your goal for your car. Just because it's possible doesn't always make it a good idea. If you're planning on racing it or care about the loss of power/performance--I wouldn't go bigger than 16's. Even though i do understand the love of bigger rims :)