You should find it in your Project directory:
AvP2\AvP2\cshell.dll
Have you got your directory path set up properly in the Working Directory under Edit >Options >Run? I'm guessing you have. It should be directly where the game is installed. My game is on E:\AvP\, so for me the Working Directory is:
E:\AvP2\
This is different to the 'Project Directory' that you set up in the Processing Options before you compile the map (Ctrl+P) and is the location where all the Project Assets were unpacked to when you ran Unrez.bat. Once again, my Project Directory is:
E:\AvP2\AvP2\
See if that helps you at all.
By the way, once compiled, you can run the map by pressing: Ctrl+Alt+R
That's really as much as I can tell you.
-Windebieste.
EDIT: Oh, just a small addition; and it may make a difference to you. In the Edit >Options >Run, leave the Program Arguments as default: -rez AVP2 +runworld %WorldName%. If you choose to continue with advanced editing, you can add the argument -nosnapnocsg to that line to really open up DeEdit's powerful geometry editing mode to its fullest. It's tricky, but its worth it.