NOTE: Xara's Align functions take a little getting used to. Left aligned objects will align to the left most object, regardless of the order of selection. Right aligned objects will align to the right most object. The same holds true for  top or bottom aligned objects.

Align the first bitmap to the left of the panel and the last bitmap to the right of the checkered panel.

Vertically align all the bitmaps over the checkered panel and Align > Distribute Equi-spaced the bitmaps horizontally. The outline circles on the bottom of the illustration represent the bitmaps.

When you have all your bitmap ducks in a row, so to speak, Copy the checkered background group, and all the bitmaps, to the Clipboard. Save your work.