Validation Of Two Fields Against A Specific Range

I am using Access 2007. This is the problem; I have a warehouse divided into four departments North, East, South, and West. Each department is assigned its own storage location range North is N1-N1000, East is E1-E1000, South is S1-S1000, and West is W1-W1000. On the access input form of my database are two fields, one combo box field for Department and one combo box field for location stored.

When the user is updating the data base for parts received or shipped, the user must enter the department and location stored to correctly debit or credit that department. The location stored entered must be assigned to the department. (Example: dept. is north and storage location is N65, the user enters D65 instead, error message is displayed, "you have entered the wrong location").

What I need is instructions how to write the code to check the fields to verify location stored matches department, and display a warning message. How do I do this? I have a table with department names and storage location ranges.