How do you add javascript actions to form fields

Hi all!

I have a mailing list setup but I'd like to have the labels for the various fields within the input boxes (like when you see a search box and it says 'search') and I'd like to be able to do a onFocus that would clear that value.

I know I can do a onFocus and onBlur but I can't seem to figure out how to get these actions attached to a particular field.

Does anyone know a way to do this or maybe some alternate method? Thanks!