When you type perldoc you're really executing perldoc.bat, which looks like

@rem = '--*-Perl-*--
@echo off
if "%OS%" == "Windows_NT" goto WinNT
perl -x -S "%0" %1 %2 %3 %4 %5 %6 %7 %8 %9
goto endofperl
:WinNT
perl -x -S %0 %*
[download]

So the first perl.exe that is found first in your %PATH% (v5.8.7) is what gets executed (even if perldoc.bat belongs to the v5.8.3 perl), but at the same time, through win32 specific magic, C:\ora10\perl\5.8.3\lib/MSWin32-x86-multi-thread/ get added to the top of @INC, so when perldoc uses Config, Config croaks (correctly) because it doesn't match the perl that's loading it.