OK after having a problem with installing the damn mod I have found a way to make it work.
1st of all, download all the fies from the Files section at
http://equilibris.celestialheavens.com/eng/downloads.html except the updates_sfx.exe
Make a backup copy of the heroes4.exe, campaign_editor.exe then install those new EXE files. Open up the install_equilibris_v3.51.exe file with WinRAR or 7Zip and unpack all the stuff to the main folder.
Open up the Command Prompt and go to the HoMM4 main folder using cd command, if it's at the other partition then 1st type the partition letter (For example if you have the game at D partition then just type D:)
Now here's the fun part.
IF you are in the main game folder type in
delta2bin heroes4.exe heroes4eq.exe mod351.patch
and
delta2bin campaign_editor.exe campaign_editor_eq.exe campaign.patch
This will create a separate file which includes the Equlibris mod to it.
If you run it, you will have the Equlibris text at the lower left screen in menu.
Warning! Do NOT change the resolution, otherwise your screen will turn black at the next run if you do this