Just use the formula option with an expression such as:
YourTable::R_Vehicle_Make ≠ YourTable::V_Make
This assumes that you are comparing the value of the first field to the value of the second. If you need to confirm that the value in field 1, matches 1 of the value list options available for field 2, this can also be done using the IsEmpty, FilterValues and ValueListItems functions to check to see if the field matches one of the listed values.
Thank you, just what I needed!