Digital BW, The Print

Hi, this is a bit OT, but it is a problem for me, if I want to print b&w 
images:

If I open an image running PS  (6 or 7) in the classic mode of OS 
X the image uses to open with weird color mistakes, e.g. images 
will have strange colored  horizontal lines or will pop up with 
different colored rectangles, which change color and place with 
each operation I start in PS (they jump within the picture). Makes 
no difference whether I open a RGB or a greyscale picture, also 
greyscales have colored mistakes. 
This is a persistent problem even after a clean reinstall 
procedure of OS X  and PS .
The problem does appear with PS 6.01 and with 7.01 too, but 
only in the Classic mode, it does not appear if I open the same 
images in the native OS 9.2 or  OSX mode (neither with PS6 nor 
with 7).
Has anybody experienced anything like this ??  
I´m on a G4 400 Mhz, 1 GB RAM, 750 MB or so allocated to PS.
Strange, isn´t it?
Thanks
Bernd