It appears that the first check for Windows XP sets the ERRORLEVEL to 0 so any other checks are invalid. Here is the latest code I am able to get to work on every OS I have tried it on.

code:
@ECHO OFF
IF NOT "%OS%" == "Windows_NT"  GOTO WIN9X
VER|FIND /I "XP" >NUL && IF %ERRORLEVEL% EQU 0 GOTO XP
IF not "%ALLUSERSPROFILE%" == "" GOTO WIN2K
IF "%OS%" == "Windows_NT"      GOTO NT4
GOTO END
:XP
ECHO Found Windows XP
REM Or what ever command you want to run.
GOTO END
:WIN2K
ECHO Found Windows 2000
REM Or what ever command you want to run.
GOTO END
:NT4
ECHO Found Windows NT 4
REM Or what ever command you want to run.
GOTO END
:WIN9X
ECHO Found Windows 9x
REM Or what ever command you want to run.
GOTO END
:END