red Xs and text reflow when passing to PC users

[Melanie]

When I receive Word rtf files from my clients, all the graphics are
missing and in their place I get large red Xs inside space holding
boxes. My PC coworkers open the same file and they see the graphics.
Also, often after I have spent hours formatting text in multi-page
docs, when I send them to my clients and the documents are opened on
PCs, the text is reflowing so that the pages and columns do not match.
Is this really a PC/Mac problem or could I have preference settings
that need changing?

Thanks!