Hi Mr. X,
if you use an analog video cable and have a monitor with more than XGA resolution, then it might be wise to invest into an ATI/AMD graphics card. Intel has crippled the RAMDAC in the video portion of their CPUs, so trying full HD gives a bad picture quality.
Digital video outputs are okay (DVI, HDMI or DP), but OS/2 might not like all variants (and only one at a time anyway).
There was only a very limited set of older ATI cards where a two monitor setup (VGA + DVI) was supported under OS/2 by the SNAP driver. Both screens must have the same resolution, the desktop can be either cloned (same content) or (extended side by side); I used it with the maximum (given by DVI) resolution of 1920x1200 pixels and 16.7 million colors.
Greetings,
Sandra-Asja