Hi Frank,
What ever version of Xara you use it will treat all bitmaps in RGB. The screen colour values use RGB so when Xara started up they used the RGB values at all times which will cause you problems when import CMYK bitmap. Having said that the PDF export will always convert the given values of your work correctly and accurately. What have you got to use another programme to convert your bitmap to RGB like Gimp or some other free programme like that.