Hi,

If the image was placed to the drawing as External reference, than you need to place the attached image (JPG, BMP...) to the same folder on your Mac where you put the drawing.
It is better to use ETRANSMIT command on Windows to create archive with DWG and all attachments, than extract archive on Mac.
If the image was inserted as OLE object, than you will be not able to see it on Mac, OLE is not supported on Mac OS X.

Maxim