You need to make sure that the Airport Extreme recognize your disk.
I only know the mac version of the airport utility version, but i assume that the windows version also have a wizard to setup.
The shared folder name should not contain spaces.
The easist way is to set tthe secure access to "With Airport Extreme password".
But this means that everybody who can access the disk will have access to everything.
Find out what the AE IP address is (shows on first page)
At windows 8:
Start file explorer
Click on Computer on the left side
Click on "Computer menu" on top of the window
Choose "Add a network location"
Then : next - choose a custom network location - next
Fill in :
\<IP address of AE>,<shared foldername>
or
\<AE name><shared foldername>
Note the < and > are only markers (do not fill in)
So for example
\192.168.1.1\Disk
Click next- if OK windows will ask you for a password.
If you use "With Airport Extreme password" then you can put everything as username (you do have put something in (windows require it,but the AE will ignore it)
Fill in the AE password for the password.
Answer following questions (pretty straight forward) and you have a shortcut to the disk
Sorry for the typo's. Spelling checking does not works Ok yet.
Hope it helps