1. Step If you installed Skyrim via Steam, go to
C:\Program Files (x86)\Steam\steamapps\common\skyrim\Skyrim – this path could be different depending on where exactly you installed Steam. If you do not have Steam, open up your Skyrim folder
2. Step Right-click on Skyrim.Prefs.ini and click on Open With, then select “notepad” or “notepad++”
3. Step Scroll down until you find [Display] then look for iSize H and iSize W
4. Step Replace the entries iSize with the size of your desktop. Simply multiply your current resolution e.g. with the number of your monitors e.g. 1920 x 3 = 5760
iSize H=5760
iSize W=1080
If you are using 3 monitors in portrait mode with the resolution 1440 x 900 then you would enter something like
iSize H=2700
iSize W=1440
Over at widescreengamingforum.com you can find a bunch of nice hacks to get it working, but it should work quite nicely without the hacks by now.