Alright, your using the ACME plate maker correct?
If thats what your using, make up the plate you want and copy and paste the image into paint.
Now, open "Page setup..." from the File menu.
At the bottom right of the window should be a set of options titled "Scaling". Make sure the the green button next to the "Adjust to:" box is checked. Now, change the 100% in that box to 20%.
Select "Ok" and print it.
It'll scale the image down perfectly to fit a 1/24 car and still keep all the clarity.