To split an image frame into equal sized rows and columns, select it on the canvas. Choose Image Tools from the menu - the Splitter option will appear.
Type in the number of rows and columns to create, and set the spacing between the resulting frames. Click Apply Split when you have completed your choices.
Image frames containing a photo can also be split. This is useful if you have a series of equal-sized photos to place in a perfect grid - use one to set the region, split it, then replace the extra copies of the original photo.