checkbox must always be checkd

hello guys,

i am trying to create a page with two radiobutton and two checkboxes. the functionality is, the checkbox must automatically be checked if the corresposding radiobutton is clicked. also while the radiobutton is checked, one must NOT be able to uncheck the checkbox. finally, when a different radiobutton is clicked, then the previously clicked checkbok must be released ( unchecked). i am not able to get the final functionality

help is greatly appreciated

thanks

where $ is nothing but Document.getElementByID()
aand the colort.getDisplay whatever is nothing but the database name of the checkbox

Here is the code......