howto align mount holes in 2 pcb the right way?
Use DXF... (it's designed for this)

DXF is a file format. It stands for Drawing Exchange Format... as in exchanging CAD data between systems.


Export your OrCAD PCB outline and drill holes as a DXF drawing
Import your new DXF as a layer into your EAGLE layout
Use the new layer to align your EAGLE parts (you may need to do this inside of a part if you are footprinting a shield template)
Remove or disable the drawing layer (it's just a reference, EAGLE can't do anything else with it)


DXF import in EagleCAD

Try the importdxf ulp that's up on 
www.cadsoftusa.com -&gt; Downloads -&gt; User Language Programs

All you have to do to use it is type RUN followed by enter in one of the
editors. Browse to the ULP and hit open. The ULP will now run and
present you with an easy to follow dialog.

Alternatively...

...use an in-between format. I found that inkscape (freeware) is good at reading DXF and can convert to HPGL format. HPGL format is easily converted to EAGLE script format.