Lines missing from printouts

I am using Visio Professional 2002 on Windows XP Pro SP
1. My computer is an IBM ThinkPad T30 with 512 MB of
RAM. I am printing to an HP LaserJet 8150DN over a
network using the 8150 postscript printer driver.

I am using Visio to draw block diagrams consisting of
lines and shapes. When I print, all single lines (drawn
with the Line Tool), no matter how thick, are missing
from the printout. All shapes, dragged from a stencil,
appear fine, even if their line thickness is just 1 pixel.

How can I make lines appear on my printouts?

Thanks,
Mark