If you choose DOS as the host mode, you are asked if you want to copy the most recent version of the Microsoft mouse driver, MOUSE.COM. (The mouse interface is built into the OS/2 environment.) This driver is written for the Microsoft Mouse, but it will work with any 100%-compatible mouse or pointing device.
If you currently use a Microsoft Mouse, you already have a mouse driver on your hard disk. SETUP places the mouse driver in the directory for real-mode files that you specify later. This directory is probably not the location of your current mouse driver. If you want to use the new driver, be sure to copy it to the appropriate directory after you leave SETUP.