Xway doesn't yet have float-left and float-right boxes, but they wouldn't help with placing text over an image.
Your link doesn't work for me, but one way to place text over an image would be to put the image inside a container box (div) and add a second box with text within the container. Then set the second (text) box to have absolute position.
Generally, you need to be careful when using absolute position: it's not a good idea to use absolute positioning as your primary way of positioning items, but I think it should work fine in this case.
Using a container for the image (and text box) will prevent the image from being used inline with text. It will need to stand on a separate line.