1)You should have Doom 2 Full version, not any demo or shareware.
2)You own doom2 or downloaded it, and have it installed on your computer.
3)Then go to this URL:
http://64.0.20.220/gbdoom/zdoom122.zip and download that file
4)Now download “GBDOOM.ZIP”
5)You downloaded both zdoom.zip and gbdoom.zip and exctracted (unzipped) it into the Doom2 folder
(This should give you “zdoom.exe”)
6)You right clicked on the z-gbd2.bat file and removed D:\games\doom2 from behind zdoom.exe and clicked apply.
7)Click the Doom2 folder where evrything should be
8)Right click the file Z-gbd2.bat
9)click on Properties
10)Click on Program or Edit
11)Click the cmdline space, type this…
zdoom.exe -file zdoom.wad gbdemo.wad gbgfx.wad colmaps.wad -deh gbd2.deh
12)Now click the batch file space and type this…
zdoom.exe -file zdoom.wad gbdemo.wad gbgfx.wad colmaps.wad -deh gbd2.deh
13)Click Apply
their now that should work