@Dave—

Mehdi has a few plug-ins that ship with Xara. Off the top of my head, I think he has Classic Eraser (for making an alpha in an image based on color), but he also offers a lot more Xara compatible plug-ins for free HERE.

You might want to check out "Blots" and "Kaleidoscope" because I think these might give you the seamless tiling you'd want for making textures.

I could be wrong, but they're free. Hey.

-g