How can I disable the overwrite function in IE?

Sometimes when I am composing a post here and then proofread it before hitting Submit, the new sentence will start overwriting the old one. How can I prevent this? My browser is IE 6.

Hitting the Insert key on your keyboard (usually located just above Delete, to the right of Backspace) toggles overwrite mode on and off. This works just about everywhere in Windows and isn’t a special function of IE.

Ah, many thanks.