Character counter for MS Frontpage 2003 forms

Hello. This project requires to make a script that indicates how many characters have been entered in text field and will stop from writing further than a set limit. This script would need to be adaptable in the future by me so that i can change the character limit. It should be able to be used for different forms and fields, so again, i would like to receive indications what i need to change to be able to use it in different places. IMPORTANT: it should be compatible with MS Frontpage 2003 script forms. I tried one counter js from the internet and the form stopped functioning as a result. I will probably need some assistance as to how to implement this into my website.