How to have widgets show only posts of a specific category.

Hi,

I’ve a customer who wants to post posts that will under certain conditions show using either Latest News or Calendar widget BUT NOT BOTH.

For example, he wants to use the calendar to display only accounting related deadlines (say a post of category ‘deadline’) while he wants the latest news widget to show only posts with category ‘latestnews’.

Is this possible without using a plugin? [I only ask about not using a plugin as for some reason I think it shouldn’t need one and would prefer to just add a reference to the category to be shown…]