Yes there is a way.
Let us assume the field name is:
My Field
First you must make the field "Required"
Then in "Validation Rule" type the following:
Len([My Field])>1 And Len([My Field])<5
Then in "Validation Text" type the follwing
You must enter at least 2 and no more than 4 characters.
Save the table. If you already have data that breaks the rule then it will warn you but will still allow you to save the changes.
Hope this works for you.
Sam