You'll need to get yourself a mouse driver. Fortunately most mice are
pretty standard (at least as far as the basic functions are concerned)
so you can usually use any driver you find.
Some versions of DOS come complete with a mouse driver:
DR-DOS has DRMOUSE.EXE, which can be unloaded as well.
PTS-DOS has MOUSE.COM
MS-DOS too has MOUSE.COM, Microsoft also supply MOUSE.EXE I'm not sure if
this comes with any version of DOS.
If you don't have a mouse driver try
CuteMouse,
I've never tried it but I've heard that it's good.
Other drivers can be found on the net if you look for them, try searching
using Google.
To start the mouse driver automatically you can of course just run it
from your autoexec.bat file, you shouldn't have to supply any parameters.
Please take note that a mouse driver will obviously take up some of your
precious conventional memory.