Dunno if you have found a solution yet, but:
The Biki fails to mention that for example in Vista (and in 7) the AppData folder is a system folder and thus by default it is hidden. Can't remember if it was hidden in XP.
If you don't want to tinker with the OS settings you can open the Start menu and in Vista/7 type in the Search field:
C:\Users\<username>\AppData\Local\ArmA
Or in XP Start menu -> Run and type in the field:
C:\Documents and Settings\<username>\Local Settings\Application Data\ArmA
You can also create a shortcut on your desktop for example, right-click -> New -> Shortcut and in the next field add C:\Users\<username>\AppData\Local\ArmA\ArmA.rpt
Alternatively, and a bit more useful: you go in that C:\Users\<username>\ folder (not in any ArmAsomethinhsomething folder), select Organize -> Folder and search options (in Vista/7), select the View page and find a setting "Show hidden files, folders and drives", select it and hit Apply.
Now you should see a more lightly colored folders in there, one of them is the AppData folder.
Now you can access the rest of the file path C:\Users\<username>\AppData\Local\ArmA
The <username> is your PC username, not your ArmA user name btw..