This is a known issue between PageMaker 6.0 and LaserWriter driver 8.4 or 8.4.1. There have also been reports of what you describe occurring with Freehand 5.5 and PhotoShop 3.0.4, however, we have not been able to reproduce this issue with these applications.
A workaround is to hold the option key down when choosing Print from the File menu. The Option key forces PageMaker to use the LaserWriter driver instead of PageMaker's internal driver.
As a longer term solution, we have alerted Adobe to this issue. Apple Engineering will also be putting a workaround to this in place with future revisions of the LaserWriter printer driver.