download code

I've got an request :
http://img337.imageshack.us/img337/4533/downlzi2.jpg
one page (several files) with black background and white color font . As in the image , all should be in the center of the page.

5 (or with generated code : 6 ) lines (color : white , background : black) everything is seen , (not orange things)

first line : Requested file : 12345678912345_7.exe (always stays the same)
second line : Download code : (and box to fill in)
third line : Generate key : (centered)
forth line : Admins code : (and box to fill in )
fith line: Download file ! / generate code ! (2 buttons )
(sixth line : Generated key ( and box with 17 symbols ) directly underneath the 2 buttons )

When the admin clicks generate code : there should be a code (17 symbols)generated into a file and saved .
That code stays active untill somebody uses it .So if the admin clicks on the button if the code isn't used yet , this should also be saved into the file . Also untill somebody uses this .

And I don't want that somebody could download the file simply by putting the good name into the browser.
thats why I tought Java , but i don't know how to work it .

thanks