If it is Windows 7 Connect up the second monitor and with them both powered up right click on the desktop and select 'screen resolution'.  Click the detect button and you should now have two monitors shown.  Now set the position (above below or side to side) and resolution for each monitor.

You do not give sizes of the monitors but if you have a different sizes, I have a 23" main and a 19" for the tools, you can also move the relationship of the second monior so that the curser moves from one screen to the next without jumping up or down.  Of course that assumes they are side by side above and below will mean the curser will move left or right if not adjusted correctly.  Much easier if you have two monitors of the same size of course.

 

 

I use Poser 13 on Windows 11 - For Scene set up I use a Geekcom A5 -  Ryzen 9 5900HX, with 64 gig ram and 3 TB  storage, mini PC with final rendering done on normal sized desktop using an AMD Ryzen Threadipper 1950X CPU, Corsair Hydro H100i CPU cooler, 3XS EVGA GTX 1080i SC with 11g Ram, 4 X 16gig Corsair DDR4 Ram and a Corsair RM 100 PSU .   The desktop is in a remote location with rendering done via Queue Manager which gives me a clearer desktop and quieter computer room.