Just wondering for large size banners etc.. Most printers prefer 300 dpi but finding images at that resolution and size can be tricky. Would you do the following:

1) Enlarge the images in photoshop then import them into xara
2) Stick with what you have and output pdf-x at 300 dpi even though the image quality may be 150 dpi or less
3) Output everything no less than 150 dpi in the pdf-x settings