You can't upload them directly to Yorkietalk, but you can upload them to a photohosting site such as Photobucket. Photobucket has an application for xoom.
Photobucket Mobile Free Motorola XOOM 2 Media Edition App download - Download the Free Photobucket Mobile App to your Android phone or tablet. I use Photobucket's application for iPad, and then just copy the address for the "direct link" and paste it here on the manage attachements menu where it says, "Upload File from a URL".