Car won't shift into park - 2003 Ford ZX2

First thing I would check is the transmission fluid. It should be running and up to its normal operating temperature when you check it. If it is up to capacity, then you may need to have the transmission filter changed. They are not too difficult to change, if you're a do it yourself'er. The flat, box-looking pan on the bottom of the transmission holds the filter. You should first drain the fluid, then remove all of the bolts from around it. (It should have several bolts that run along the outside edges of the pan. After this is removed you will see your filter. Some of them just pop out by hand and some have some screws or bolts holding them in. They are a relatively cheap fix if that is causing the problem. If it is clogged, it is keeping the fluid from going to where it should. Some filters are permanent, meaning they should just be taken out and cleaned before putting it back in. You may also want to check the linkage. The linkage is what connects your shifter knob/stick in your car, to the actual lever/shifter/stick on the actual transmission. I have seen rocks and road debris get stuck on the side of the transmission, seriously limiting the movement of the lever/linkage/shift knob, etc... It is usually found on the left side of the car, running down the drivers side of the transmission. You can wiggle it from the inside of the car and let someone look underneath and it should be easily seen.
I hope this helps