Phil,
If you want the graphic to look better on the screen, go to File> Preferences and select High resolution in the Graphics Display area of the box. When you print to a good postscript printer, you will get better results than printing to and inkjet.
Also try not to stretch a graphic when using File> Place. However, you can make it smaller with no problems. I try to use the cropping tool as much as possible in PM so the file size of the graphic does not increase as it sometime will whenever you make any change to its physical size in a graphics program.
If you have the choice not to save the graphic to PM, do so. The really large graphic will link to the file when it prints. A graphic placed that way will not add any size to the PM file.
Daniel