Go to this page:
First you need to install the extended map
Then you go to extended map data:
Follow the instructions and choose the map you want to download. You download it by right-clicking the small arrow next to the map version column and choosing "Save Target as". Thus, you can save it i.e the desk or directly in WITP:AE folder.
File is a zip file , so you need to unpack it.
Basically, in my WITP:AE ART folder I create a folder called Stock Map and put all the stock map bitmaps there and put the unpacked Extended Map bitmaps into the ART folder.
Now, select the scenario fo your choosing, say DaBigBabes C.
Scroll down to the bottom of the page. You shall see two zip files named 028 and 029. 028 scenario starts on Dec 7,1941, scen 029 starts on Dec 8,1941. Say, you want scen 028.
In the same line, you should see a small arrow. Right-click it once, and choose "Save target as". Thus, you can select where do you want to save the zip file.
Unzip it. You should see a folder containing some small .dat files. Drop them in the SCEN folder of your WITP:AE installation and play the game.