How to control the text input size in textarea field

I only have 255 characters and in text area people are putting more text and it is giving error OLEdb .

I wanted to add this coding of javascript http://www.dynamicdrive.com/dynamicindex16/limitinput2.htm

to control the text input in text area field but in my files i see in templates folder then in add files then settings then variables.asp etc, and couldn't figure out where do i put this javascript. as in my asp files there are too many files are involved to create a text area and still can't find an easy way out to put this coding .

Can you pls. suggest an easy way out to control the amount of text can enter in text area field (Not the text filed as in text field you have given options but in text area you have only given height and width of text area as options and not the characters count or control of characters.,) .

thanks