That's strange, because a OKI laserwriter doesn't have this problem and neither does the epson printer when I use the gimp drivers (version 4.3.2) for epson that come with the MacOS 10.3.
But these are very slow and have bad colormanagement etc.
It only happens with vectorworks in combination with epson printerdrivers under MacOS X. It doesn't matter wich version for any of the programs I use. How can it be explained that the lines are thicker, even on screen!?