Usually professional printers want your work in TIF or EPS format (or both), split to CMYK. When you split to CMYK you get four grayscale images representing those colors.

If you want to turn a color image into black and white, grayscale, etc. choose Format, Data Type and select the correct option, then save it. Black and white can yield some very stark looking results, are you sure they don't want grayscale? I'd check to be double sure.

If your printer wants you to end up with a 300 pixels per inch image, make sure your new canvas is 300 pixels per inch. PI defaults to 72 dpi and that can cause great disappointment later on if you're not aware of it.

Stephanie's PhotoImpact Tutorials
PhotoImpact 8 and 7 Classes