With eps images, what you typically see in Word is a preview image that is saved in the eps file. Unless you're using a postscript printer, the preview image (which is usually of low quality) is what will be printed. With a postscript printer, however, the full eps data will be used, giving an output that is of potentially much higher resolution than Word 2010 is capable of (Word's max is 220dpi, which is somewhat low).

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]