Javascript - dynamic form text limit help

Hi, i hope someone out there can help me create or point me in the right direction, to allow me to do the following:

I want a textarea in my form, which has a text limit on it that the user can see, i have this working having used some great code from Dynamic Drive (http://www.dynamicdrive.com/dynamicindex16/limitinput.htm)

But i want that textarea to remain disable until one of two radio buttons is selected, as well as that i want the text limits to go up or down depending on which radio button.

Hope someone can help, as i’m start to go abit mad!

Thanks