Need Dual EMC Installation

Dear Folks,

Presently have a CNC Sherline Mill that I've been trying to set up.
Would like to ask group if anybody has installed both Debian & Ubuntu
EMC to PC?? I can install Debian with CD but not sure how to prepare
the HD partition so I will be able to install Ubuntu on the same HD
and have a window to choose which to open??

The Debian EMC installs nicely as does the Ubuntu EMC using CDs.
However I seem to be missing something as one will eliminate the
other when installed individually, and vise versa. What is left is the
EMC version that you last installed.

Probably has something, I suspect, with preparing the HD partitions
when asked by the EMC installer. Can anybody help? Would like to have
both EMC's present on the HD to compliment each other and to be able
to choose which one to open.

Would certainly appreciate if somebody could direct me in what
procedure to take or just tell me where to go?

Your assistance concerning this matter would be very much appreciated.

Pete - Newby Senior C